POWER PLANT TESTING 



WORKS BY 
PROFESSOR J. A. MOYER 



Published by McGRAW-HILL BOOK COMPANY 

Power Plant Testing. 

A Manual of Experimental Engineering. 
Svo, xiv + 422 pages, 271 figures. Cloth, 
$4.00. 

Published by JOHN WILEY & SONS 

The Steam Turbine. 

A Practical and Theoretical Treatise for 
Engineers and Designers. 8vo, ix+370 
pages, 225 figures. Cloth, $4.00. 

Descriptive Geometry for Students of En= 
gineering. 

(Principally "Third Angle" Methods.) 
8vo, viii+204 pages, 128 figures. Cloth, 
$2.00. 



POWER PLANT 
TESTING 



A MANUAL OF TESTING ENGINES, TURBINES, BOILERS, 

PUMPS, REFRIGERATING MACHINERY, FANS, FUELS, 

MATERIALS OF CONSTRUCTION, ETC. 



JAMES AMBROSE MOYER, S.B., A.M. 

Member American Society of Mechanical Engineers, Mitglied c/es Vereines deutscher 
Ingenieure, Member of the Franklin Institute, American Society of Refriger- 
ating Engineers, American Institute of Electrical Engineers, etc. , Assistant 
Professor of Mechanical Engineering in the University of 
Michigan, formerly Engineer, Steam Tin- bine Depart- 
ment, General Electric Company, and Engineer, 
Westinghouse, Church, Kerr &• Company 



McGRAW-HILL BOOK COMPANY 

239 WEST 39TH STREET, NEW YORK 

6 Bouverie Street, London, E.C. 

1911 






'>* 



Copyright, 1911, 

BY 

McGRAW-HILL BOOK COMPANY 



• 






THE SCIENTIFIC PHESS 

ROBERT DRUMMOND AND COMPANY 

BROOKLYN, N. V. 



€"CI.A2 97(>63 



PREFACE 



In the preparation of this book the object in view has been 
primarily to give in a small volume, somewhat in detail, the 
generally approved methods of testing engines, turbines, boilers 
and the auxiliary machinery usually found in power plants, 
as well as to present more or less complete descriptions of the 
various kinds of apparatus used and the calibrations required for 
accurate testing. In addition to this subject-matter, chapters 
have been prepared on the testing of fuels, refrigerating and 
hydraulic machinery, as well as on the proper methods and 
the machinery to be used in making tests of the strength of the 
materials commonly used in the construction of buildings. 

As a book for students in laboratory courses it is intended 
particularly for use in large classes in which at the beginning of 
the laboratory periods it is necessary to begin at the same 
time a number of different experiments and tests. On this 
account care has been taken to state as clearly as possible the 
descriptions of the apparatus to be used and the precautions to 
be observed to secure accuracy in the results. Students should 
be expected, however, to rely to some extent on their own 
initiative. 

In most respects the book is probably complete enough in 
descriptive matter and in general instructions so that very little ' 
lecture-room work is needed for at least elementary courses. 
It is the author's opinion that students in experimental engineer- 
ing laboratories should not receive a great deal of assistance in 
planning and conducting tests. Sometime they must learn to 
be resourceful and independent of the "school" type of instruc- 
tion and obviously the sooner this is appreciated by both instructors 
and students the greater will be the benefits. At least for very 
small classes the better plan is the one advocated years ago by 



VI 



PREFACE 



a famous educator, that students working in laboratories when 
assigned the work of testing a machine, a new type of aeroplane 
engine, for example, should have very simple instructions such 
as: "Make tests of this new type of engine, find out what you 
can about it and report your results." It is to be hoped that the 
particular method of teaching in laboratories known familiarly 
as "feeding with a spoon" has disappeared in present-day 
instruction in technical schools and colleges. 

Quite a large part of the training required for one to become 
accurate and reliable in the work of observing and interpreting 
the results of tests of machinery consists in becoming familiar 
with the details of the adjustment and calibration of the various 
instruments, so that they may be used intelligently. 

Although in the arrangement of the chapters the use of the 
book by students was given the most careful consideration, yet 
as a whole the needs of the "practical" man were not lost sight 
of, and it is hoped that the author's experience when working 
with this group of readers in testing both large and small power 
plants has helped to make the book interesting and helpful to 
them. The book is intended to be also a manual giving useful 
information in a more or less limited way to those professional 
engineers having the advantages of a technical training, but who 
are not thoroughly familiar with the most up-to-date methods 
of testing. 

In many cases not nearly all the results that should be calcu- 
lated to make up a complete report are mentioned. It is the 
opinion of the author that in a text-book it is desirable that no 
more than very general instructions should be given regarding 
the conduct of the test, the quantities to be calculated, and the 
form and tabulations expected in a report. Such details should 
be left in the hands of the instructor. Because the size of the 
book was limited it was necessary to omit explanations of the 
methods of calculating many interesting and more or less appli- 
cable results from tests. In the more extended courses it is 
believed that the instructors can readily fill in these omissions. 

The author is particularly indebted in the preparation of this 
book to Professors M. E. Cooley, J. R. Allen, C. J. Tilden, and 
E. D. Campbell, of the University of Michigan; Professors I. N. 
Hollis and L. S. Marks, of Harvard University; Professor H. W. 
Spangler, of the University of Pennsylvania; Professor W. F. M. 



PREFACE vii 

Goss, of the University of Illinois; Professor C. H. Peabody of 
the Massachusetts Institute of Technology; Professor L. V. 
Ludy, of Purdue University; Professor A. M. Greene, of Rens- 
selaer Polytechnic Institute; Professor C. C. Lorentzen, of New 
York University; Professor E. J. Fermier, of the Mechanical and 
Agricultural College of Texas; Professor E. A. Fessenden, of the 
University of Missouri; Professor F. H. Sibley, of the University 
of Alabama; Dr. C. P. Steinmetz and Mr. Richard H. Rice, of 
the General Electric Company; Mr. H. R. Kent Vice-president, 
Westinghouse, Church, Kerr & Company; Mr. J. R. Bibbins, of 
The Arnold Company; Mr. R. A. Smart, of the Westinghouse 
Machine Company; Mr. St. John Chilton, of the Allis-Chalmers 
Company; and Messrs. G. E. Wallis, J. E. Emswiler, F. P. 
Maloney, J. R. Bazley, and E. D. Connell, of Ann Arbor. 

The short steam tables given in the Appendix have been 
taken, with permission, from Allen and Bursley's "Heat Engines." 
In many cases, particularly regarding engineering practice abroad, 
Pullen's ''Engines and Boilers " has been found very useful. 

J. A. Moyer. 
Ann Arbor, Michigan, 
August, 191 1. 



INTRODUCTION 



Tests of the machinery in a power plant are usually made 
to determine the capacity and efficiencies of its various units 
when operating under certain definite conditions. In recent 
engineering practice manufacturers and contractors are generally 
required to make certain estimates and guarantees of the capa- 
city and efficiency of the various kinds of machinery supplied. 
This is exactly equivalent, in other words, to agreeing to pro- 
vide for doing a given unit of work under specified conditions 
at a definite cost. The purchaser, on the other hand, for his 
protection, finds it necessary to determine from the results of 
reliable tests whether the " guarantees " can be obtained. 
Obviously, then, the importance of knowing how to make 
careful and reliable tests, of which the results will not be 
questioned, cannot be overestimated. 

Tests of power plants as a whole are also necessary and 
should be made from time to time in order to determine what 
results can be obtained from an economic viewpoint when 
operating under the existing conditions; and also for finding 
out what saving can be obtained by changes in the operating 
conditions or by the installation of more efficient auxiliary 
machinery. From the viewpoint of determining whether or 
not it is economical to replace old equipment with new, tests of 
old installations are relatively more important than those of 
newer ones, because usually it is out of the question to rele- 
gate practically new machinery to the scrap-heap. The great- 
est importance of such tests is due, however, to the fact that 
they show how nearly the existing conditions of operation 
conform to those of standard engineering practice, and to those 
obtained in other plants operating with the greatest success. 



X INTRODUCTION 

Practice tests in the laboratory are intended to show to 
students by actual experience the best methods for investi- 
gating the problems arising in the operation of plants, how to 
work out in a practical way the doubtful points in designing 
and constructing machinery, and, above all, to think accu- 
rately and systematically in such matters. 

Procedure for making accurate tests may be stated as 
follows : » 

i. Procuring a suitable standard testing equipment. Any 
instruments and apparatus not well known to engineers gen- 
erally and which are of doubtful accuracy or sensitiveness should 
always be avoided. Remember that a single element of uncer- 
tainty may vitiate the acceptance of the results of a test of 
otherwise undoubted accuracy. 

2. Careful calibrating of instruments before a test, so that 
the greatest possible errors of the tests are definitely known 
and that proper allowance can be made in the results. 

3. Systematic recording of observations. 

4. Recalibrating of instruments after a test to determine 
whether there have been any changes in their accuracy. 

5. Preparing of a report embodying data, results and con- 
clusions. 

6. Tabulating and plotting on cross-section paper the 
important results. This plotting is not only for the purpose of 
showing the results graphically, but also for the purpose of 
providing a check or a method of eliminating errors in obser- 
vations or in calculations. The skill of an engineer in testing 
is shown more than in any other way, by his ability to check 
results. If after applying various checks, usually by means of 
plotted curves, the results for varying conditions are found 
to agree, the engineer is able to tell definitely whether or not 
his tests are reliable. 



CONTENTS 



PAGE 

Introduction i 

I. Measurement of Pressure i 

(i) Manometer or U-tubes i 

(2) Bourdon Gage 6 

(3) Diaphragm Gage 8 

(4) Vacuum Gage 9 

(5) Recording Gage 10 

(6) Calibration of Pressure Gages 12 

Dead-weight Gage Testers 13 

Mercury Columns 18 

(7) Calibration of Vacuum Gages 21 

(8) Calibration of Low-pressure Gages 21 

(9) Draft Gages 23 

II. Measurement of Temperature 25 

(1) Mercurial Thermometer 25 

(2) Alcohol Thermometer 26 

(3) Calibration of Thermometers 26 

Compared with Standard Thermometer . 26 

Compared with Temperature of Steam 29 

(4) Corrections for Stem Exposure 31 

(5) Recording Thermometers 34 

(6) Pyrometers 36 

a. Thermo-electric 36 

b. Mechanical 38 

c. Optical 39 

d. Calorimetric 41 

(7) Seger Cones 43 

III. Determination 'of Moisture in Steam 46 

(1) Throttling Calorimeter 47 

(2) Separating Calorimeter 53 

(3) Combined Separating and Throttling Calorimeter for 

Low-pressure Steam 57 

(4) Electric Calorimeter 61 

(5) Barrel Calorimeter 62 

(6) Calibration of Calorimeters 65 

xi 



CONTENTS 

PAGE 

IV. Measurement of Areas 66 

(i) Planimeters 66 

a. Polar 67 

b. Coffin 75 

c. Rolling 78 

(2) Testing of Planimeters 79 

(3) Durand- Bristol Integrating Instrument 80 

V. Engine Indicators and Reducing Motions 85 

(1) Indicators : 85 

a. Watt 85 

b. Thompson 86 

c. Crosby 88 

1. Inside Spring : 89 

2. Outside Spring 92 

d. Star Brass 93 

e. Tabor 93 

/. Bachelder 95 

g. Cooley-Hill Continuous Indicator 99 

h. Optical 101 

(2) Calibration of Indicator Springs 105 

(3) Tests of Drum Springs 112 

(4) Reducing Motions 113 

a. Pantograph or Lazy-Tongs , 115 

b. Parallel Motions for Indicators 116 

c. Reducing Motions Attached to Indicators 118 

(5) Calculation of Indicated Horse Power 118 

VI. Measurement of Power 122 

(1) Absorption Dynamometers 122 

a. Prony Brake 123 

b. Rope Brake 125 

c. Alden Dynamometer 127 

d. Water Brake 128 

(2) Electric Generators and Motors as Dynamometers. . . 131 

(3) Transmission Dynamometers 133 

Goss 134 

Webber 136 

Emerson Power Scales 138 

Flather 140 

VII. Measurement of the Flow of Fluids '. 142 

(1) Air and Other Gases 142 

a. Meter ; 142 

b. Pitot Tube 143 

c. Orifice 146 

d. Calorimetric Method 146 

e. Anemometers 147 

(2) Steam — Wet, Dry, Saturated, and Superheated 148 

a. Orifice 148 

b. Meter 149 



CONTENTS Xlii 

PAGE 

(3) Water . 150 

a. Meter 151 

b. Automatic Weigher 152 

c. Venturimeter 155 

d. Orifice 158 

e. Weir 1 59 

VIII. Calorific Value of Fuels 162 

(1) Fuel Calorimeters ■ 162 

a. Calculation of Water Equivalent 163 

b. Mahler 164 

c. Atwater 167 

d. Emerson 168 

e. Parr 169 

/. Carpenter 172 

g. Junkers 174 

(2) Calorific Value from Analysis 177 

(3) Proximate Analysis 178 

IX. Flue Gas Analysis 181 

(1) Sampling Bottles and Tubes 182 

(2) Fisher's "Orsat" Apparatus 188 

(3) Allen-Moyer "Orsat" Apparatus 190 

(4) Calculations 192 

a. Weight of Air 194 

b. Weight of Gases 195 

(5) Recording Apparatus for C0_, 196 

X. Boiler Testing 200 

A. S. M. E. Rules and Data Sheets 202 

XL Steam Engine Testing 229 

(1) Mechanical Efficiency and Friction 229 

(2) Valve Setting 230 

a. Slide Valve 230 

b. Corliss Valve 234 

(3) Clearance Tests 240 

(4) A. S. M. E. Rules and Data Sheets 241 

(5) Heat Balance 257 

(6) Thermal Efficiency 259 

(7) Entropy-temperature Diagrams. . , 262 

(8) Willans' Law 274 

(9) Steam Engine Lubricators 276 

XII. Testing of Steam Turbines and Turbine Generators. . 279 

XIII. Methods for Correcting Steam Engine and Steam 

Turbine Tests to Standard Conditions 296 

XIV. Gas Engine and Producer Tests 306 

(1) Indicated and Brake Horse Power. 306 

(2) Gas Engine Indicators 307 

(3) Measurement of Fuel 308 

(4) A. S. M. E. Rules and Data Sheets 310 



xiv CONTENTS 

PAGE 

(5) Abnormal Indicator Diagrams 316 

(6) Gas Producers 319 

(7) Capacity and Efficiency of Gas Producers 324 

XV. Tests of Ventilating Fans or Blowers and Air Com- 
pressors 325 

XVI. Tests of Refrigerating Machines 337 

(1) Compression System 338 

(2.) Absorption System 345 

XVII. Tests of Hot-air Engines 350 

XVIII. Tests of Hoists, Belts, Rope Drives, and Friction 

Wheels 353 

XIX. Tests of Hydraulic Machinery 356 

(1) Belt-driven Feed Pumps 357 

(2) Steam Feed Pumps 358 

(3) Impulse Wheels. . . ._ 363 

(4) Water Turbines 366 

(5) Hydraulic Rams 367 

(6) Pulsometers 370 

(7) Injectors 372 

XX. Tests of the Strength of Materials 376 



POWER PLANT TESTING 



CHAPTER I 



MEASUREMENT OF PRESSURE 



The simplest instrument used for measuring pressure is a 
glass tube bent into the shape of the letter U, as illustrated 
in Fig. i. When such a tube, called 
technically a manometer or U-tube, is 
partly filled with a liquid, usually water 
or mercury, and is connected at A by 
means of tubing to the vessel in which 
the pressure is desired, there will be ob- 
served a difference in the level of the 
liquid corresponding to the pressure. If 
the end of the tube at B is open to the 
atmosphere, then the difference in the 
level of the liquid in the two legs measured 
in inches, multiplied by the weight of a 
cubic inch of the liquid in pounds, gives 
the difference in pressure in pounds per 
square inch between that in the vessel 
and atmospheric pressure. When the level 
in the leg B is higher than in A then the 
pressure measured is greater than atmos- 
pheric and is called gage pressure to 
distinguish it from ' the other condition 
when the level in the leg A is higher than 
in B; that is, when the pressure is less 
than atmospheric. In the latter case we 
speak of vacuum or negative pressure. 

As such instruments are usually constructed, a scale suitably 




Fig. i.— A U-tube. 
The Simplest In- 
strument for Meas- 
uring Pressures. 



POWER PLANT TESTING 



M 




graduated for measuring the difference between the levels 
of the liquid in the tube is placed between the two legs, as 
shown in Fig. 2. Still another type is illustrated in Fig. 3. In a 
manometer of this kind one leg can be made very short if it is 
correspondingly large in diameter. If the scale is adjusted so that 
the level in the short leg is at the zero of the scale, then the 
level in the long leg will indicate directly 
inches of pressure or of vacuum as the case 
may be. A typical vacuum gage of the same 
kind is illustrated in Fig. 4. The end of the 
tube corresponding to the short leg in Fig. 3 
is shown at A. When manometers are to 
be used for pressure or vacuum measure- 
ments of steam, a condenser (C, Fig. 5) is 
often employed to prevent the passage of 
steam into the glass tube in which it would 
form a water column on the top of the 
mercury for which a correction l would have 
to be made. To be effective the condenser, 
C, must always be partly filled with water. 
Manometers or U-tubes of very small diameter 
when filled with mercury may be affected by 
capillarity to such an extent that in order 
to obtain the true height corresponding to 
the pressure, a correction must be added. 
It is not at all unusual to find manometers 
used for vacuum gages to be comparatively 
small in diameter, and unless the gradua- 
tions of the scale have been corrected for 
the error due to capillarity the proper allow- 
ances must be made for all observations. 
Fig. 5 shows by a curve the values of this 
as determined by Pullen for mercury columns of 



W 



Fig. 2. — A Simple 
Manometer with a 
Graduated Scale. 



correction 
various diameters. 

Mercury columns should be read at the top of the meniscus 
and water columns should be read at the bottom. In this way, 



1 Correction for water on the top of a mercury column is most 
conveniently made by dividing the length of the water column by the 
specific gravity of mercury (13.6) and adding this equivalent length 
to the mercury column on which the water rests. 



MEASUREMENT OF PRESSURE 



except in very small tubes, the errors due to capillarity may 
be regarded as negligible. 

Conversion of Pressures. It is frequently necessary to re- 
duce pressures in inches of mercury or of water to the equiv- 
alent in pounds per square inch. Since the weight of a cubic 
inch of mercury at 70 degrees Fahrenheit is .4906 pound and 



Fig. 3. 




Fig. 4. 
Typical Mercury Vacuum Gages. 




of water at the same temperature is .0360 pound, pressures in 
inches of mercury at the usual " room " temperatures can be 
reduced to pounds per square inch by multiplying by .491 or 
by dividing by 2.035, and similarly inches of water can be 
converted to pounds per square inch by multiplying by .0360 
or by dividing by 27.78. 



4 POWER PLANT TESTING 

Kilograms per square centimeter are reduced to pounds 
per square inch by multiplying the kilograms per square centi- 
meter by 14.223, or by dividing by .0703. 

A cubic foot of water at 70 degrees Fahrenheit weighs 62.3 
pounds and at 30 degrees Fahrenheit, 62.4 pounds. At ordi- 
nary room temperature the pressure due to 2.31 feet of water is 
equivalent to one pound per square inch. 1 







:: 










t 


f 


r 


f 


i 


1 




t 


1 


i 


1 


r 


V 


3 x 


t 


5 


K 


5 


\_ 


-^ 


\, 


^ 


""--, 




0.05 0.1 0.15 0.2 0.3 0.4 0.5 0.6 



Diameter of Tube in Inches. 
Fig. 6. — Curve of Capillarity Corrections for Mercury Columns. 

Tubes used as mercury manometers must be cleaned from 
time to time by washing the inside surface with nitric acid and 
afterward thoroughly cleansing them with water. Mercury 
used in manometers should be free from impurities. Usual 

1 The unit pressure of one pound per square inch is equivalent also 
to that due to a column of air of uniform density, of which the vertical 
height in feet is approximately, 144.0 divided by the weight of a cubic 
foot of air at the temperature, pressure and humidity as observed. 
Tables of the weight of air are given on page 



MEASUREMENT OF PRESSURE 



impurities can generally be removed by filtering through a 
clean cloth of close texture or a thin chamois leather. Air can 
be removed by boiling, but by far the best method for cleaning 
mercury is by means of a mercury still. Unfortunately an 
apparatus of this kind is not available in most engineering 
laboratories. 

Pressure Gages. The large size necessary, however, for 
manometers or U-tubes, even if filled with the heaviest liquids, 
makes their use unsuitable except for comparatively low pres- 
sures. Instruments 
more desirable for 
high pressures are 
made by the applica- 
tion of some kind of 
elastic material de- 
signed to produce a 
uniform deformation 
for variations of pres- 
sure. By connecting 
a suitable auxiliary 
mechanism to the 
elastic element it can 
be made to move a 
needle to indicate on 
a graduated dial the 
degree of pressure. 
The most common 
form of such devices 
is a hollow brass or 
steel tube bent into 

the shape of an arc of a circle. It is a well-known principle that 
when a straight piece of tubing is bent into this shape the 
sides come nearer together, making the section of the tube a 
very much flattened oval. A tube of this kind is illustrated 
in Fig. 7, showing also in the right-hand corner a transverse 
section. If one end of such a tube is closed and fluid pres- 
sure is applied to the inside, the parallel sides, as at A and B, 
tend to separate and consequently there is a tendency for the 
radius of curvature of the tube to become larger, thus moving 
the end at E toward F. By connecting a suitable mechanism 




Fig. 7. — A Typical Bourdon Tube. 



POWER PLANT TESTING 



to E, the degree of pressure can be indicated. Instruments 

of this kind are called Bourdon gages. 

Fig. 8 shows one of the simplest forms of such gages used 

in power plants to 
indicate the pressures. 
It consists essentially 
of the curved tube T 
of oval cross-section 
closed at one end. 
By means of suitable 
levers and gears a 
pointer or needle P 
is made to move over 
a dial graduated or 
marked to indicate 
pressures in standard 
units as, for example, 
pounds per square in. 
(English system) or 
kilograms per square 
centimeter (Metric 
system). (Fig. 9.) 
Fig. 10 shows a form of Bourdon gage in which the amount 

of vibration of the needle due to the jarring that occurs in 




Fig. 8. — Typical Bourdon Pressure Gage. 




Fig. 9. — The Dial of a Pressure Gage. 



A Modified Bourdon Gage. 



locomotive and other portable services has been reduced to 
a minimum by supporting the pressure tube in the middle 



MEASUREMENT OF PRESSURE 




instead of at its end as in Fig. 8. This form of tube has also 
advantages for use in gages exposed to temperatures below 
freezing, since the arms can be drained of water, while the other 
form will usually hold the water that has entered. 

Gages to be used to determine the pressure of ammonia 
have the oval tube made of steel instead of brass because the 
latter material deteriorates rapidly in the 
presence of ammonia. 

Bourdon gages may be used for indi- 
cating the pressures of either liquids, steam 
or gases without observing special pre- 
cautions if the temperature is never much 
over 150 degrees Fahrenheit. If, however, 
the elastic tube in the gage is heated above 
this limit it is likely to lose some of its 
temper. When used for steam pressure, 
therefore, some form of siphon or water 
seal must always be used to prevent steam 
from entering the gage. The type of 
siphon used most commonly is illustrated 
in Fig. 11. There is always a possibility, 
however, that air carried in the steam may be entrapped at a, 
where it forms a cushion, preventing the gage from indicating the 
true variation in pressure . For this reason 
the form of siphon shown in Fig. 12 
is preferred for accurate measurements. 
In Bourdon gages any lost motion 
v y of the parts is taken up by the hair- 

] J []>>*^-r-^^ spring attached to the spindle carrying 

1^ TT O'V the pointer. 

Adjustments. The ratio of motion 
of the pointer with respect to that of 
the tube can be adjusted in most 
Bourdon gages by sliding a set-screw 
in a slot in the short arm of the rack- 
lever. In the gage illustrated in Fig. 8 
when the short arm of the rack-lever is 
made longer by adjusting the set-screw, the movement of the rack 
and also of the pointer is reduced for a given deflection of 
the tube. 



Fig. 11. — A Circular 
Siphon for Steam 
Gages. 




Fig. 12. — A U-shaped 
Siphon for Steam 
Gages. 



8 



POWER PLANT TESTING 



Sometimes when used carelessly, especially when subjected 
to pressures beyond the scale on the dial, the tube of the gage 
takes a permanent " set "; or, in other words, it does not spring 
back to its original position, and the pointer does not come back 
to the zero mark. In such exigencies and also for adjustment 
after calibration the needle can be forced off from its spindle 
— preferably by the use of a clamp or " needle-jack " made by 
gage manufacturers specially for this service — and then set 

again in position 
where it should be. 

Another kind of 
gage in which there 
is a metallic disk or 
diaphragm instead of 
a bent tube for actu- 
ating the indicating 
device is sometimes 
used. One of this 
type is well illustrated 
in Fig. 13. It con- 
sists of a corrugated 
diaphragm clamped 
around its edge by the 
flanges of an encir- 
cling chamber. Pres- 
sure applied on the 
lower side of the 
diaphragm deflects it 
upward, the amount 
of this upward move- 
ment being proportional to the pressure. By means of a con- 
necting strut S the movement of the diaphragm is communi- 
cated to a rack R connected to a small pinion attached to 
the spindle of the needle indicating the pressure on the 
graduated dial. 

Since the deflection of the center of the diaphragm is pro- 
portional to the pressure and is inversely proportional to the 
cube of its thickness, a very slight alteration in the thickness 
of the diaphragm will cause a considerable change in the reading 
of the gage. 




Fig. 13. — A Typical Diaphragm Ga; 



MEASUREMENT OF PRESSURE 



9 



Vacuum Gages. For the measurement of vacuum instead 
of pressure Bourdon gages are also very commonly used. The 
design used for a pressure gage is altered only in the arrange- 
ment of the levers moving the needle, which for vacuum meas- 
urements turn it in the same direction as for pressure (clock- 




Fig. 



-A Recording Pressure Gj 



wise) , when, as in this case, the tube is bent inward or toward 
the center of the gage instead of outward as for pressure meas- 
urements. Vacuum gages are usually graduated to read inches 
of mercury below atmospheric pressure. Absolute pressure 
in inches of mercury is the difference between the barometer 
and the reading of such vacuum gages. 



1(1 



POWER PLANT TESTING 



Still another type of pressure gages known as a compound 
gage is used to indicate either pressure or vacuum on the 
same dial. 

Recording Gages. In many modern power plants recording 
gages are used to give a graphic record on a chart of the pres- 




FlG. 



:5. — Operating Parts of a Recording Gage with a Helical Tube. 
(Bristol.) 



sure or vacuum for 24 hours. The most common type of record- 
ing gage is shown in Fig. 14. 

These gages are made with either a circular tube of oval 
section in the form of a helix as illustrated in Fig. 15, with a 
metallic Bourdon tube as shown in Fig. 16, or with a dia- 



MEASUREMENT OF PRESSURE 



11 



phragm device as in Fig. 17. The first and second of these three 
types are generally used for cases where the maximum pressure 
is greater than 3 pounds and the third when it is less. The 
recording arm is preferably attached directly to the moving 
element so that no gears, levers, or other multiplying devices 
are needed. A more compact and less expensive form of such 
gages is illustrated in Fig. 18. 




Fig. 16. — A Recording Pressure Gage Operated by a Bourdon Tube. 



The average pressure corresponding to an irregular curve 
traced on the circular card of one of these recording gages is 
obtained with a fair degree of accuracy by integrating the curve 
by means of a Durand-Bristol integrating instrument described 
on page 80. Corrections to be applied to the readings of 
these gages are of course obtained by calibrating in the same 
way as for an indicating gage. 



12 



POWER PLANT TESTING 



Still another type of recording pressure gages is shown in 
Fig. 19. 

Calibration of Gages. Until recent years when the so-called 
"dead-weight " apparatus for testing gages came into general 




Fig. 17. 



-A Low-pressure Recording Gage Operated by a" Diaphragm " 
Device. 



use, gages used in other places than engineering laboratories 
were commonly calibrated by comparison with a so-called 
test gage. Such test gages have usually somewhat finer gradu- 
ations than the ordinary gages used in practice and are probably 
also adjusted a little more accurately. They should never be 
exposed to the severe conditions of service, being intended 



MEASUREMENT OF PRESSURE 



13 



only for purposes of comparison. This comparison can be 
made anywhere by connecting the standard and the gage to 
be tested to any system of piping in which the pressure can 
be varied either by pumping a liquid, or by means of valves 
" throttling " steam, water or air under pressure. The only 
important precaution to observe is that the two gages shall be 
at approximately the same level when a liquid is used, and that 
the velocity of the fluid in the main pipe to which the gages are 
attached is negligible or is the same at the points where the 
connections for the 
gages are inserted 
in the "main "pipe. 
Test gages must, of 
course, be calibrated 
from time to time 
with some standard 
apparatus to insure 
their accuracy. A 
bench pump suitable 
for calibrating by 
comparison is illus- 
trated in Fig. 20. 

Gage Testers. In 
very many power 
plants the use of the 
test gage has been 
superseded by some 
form of gage tester 
and by this means 
the gages used in the 

plant can be calibrated directly with an absolute standard. Cali- 
brations of gages for high pressures by means of mercury columns 
are for practical reasons suitable only for laboratory work. 

Dead-weight Gage Testers. The best-known form of this 
apparatus is made by the Crosby Steam Gage and Valve Co., 
and is illustrated in Figs. 21 and 22. The latter figure shows 
a partial section. It consists of a vertical cylinder C, into 
which is fitted very accurately a piston P, of which the area, 
when new, is exactly one-fifth of a square inch. A circular 
platform upon which weights can be placed is attached to the 




Fig. 18. 



-A Veyr Compact Tpye of Recording 
Gage. (Bristol) 



14 



POWER PLANT TESTING 



upper end of this piston. The cylinder, C, communicates at 
its lower end with the reservoir R, fitted with an adjustable 
plunger working in a screw and is operated by a hand wheel. 
A pipe, T, attached to the lower part of the reservoir is pro- 
vided with unions and special fittings for attaching gages of 
various sizes. In the horizontal portion of this pipe a three- 
way cock or valve V is provided for either draining the reser- 
voir or for closing the pipe so that the liquid in the apparatus 




Fig. 



-A Combined Recording and Indicating Pressure Gage. 



will not escape when the gage is removed. In operation, after the 
gage has been attached securely, the adjustable plunger S (Fig. 22) 
is screwed down to the bottom of the reservoir R, then with 
the piston removed, glycerine or heavy oil is poured into the 
cylinder C at the same time that the plunger P is screwed out. 
In this way the reservoir can be completely filled with oil 
witout entrapping any considerable amount of air which would 
act as a cushion preventing the most satisfactory operation 
of the apparatus. 



MEASUREMENT OF PRESSURE 



15 




Fig. 



-A Bench Test Pump. 



If the area of the piston is one-fifth of a square inch then 
each pound weight 
added on the plat- 
form produces a 
pressure on the 
liquid of 5 pounds 
per square inch . 
The weight of the 
platform and pis- 
ton (usually 1 
pound) must al- 
ways be included 
in the weight pro- 
ducing the pres- 
sure. As the load 
on the platform 
is increased the 
plungermust,from 
time to time, be 
screwed in to keep the piston and platform " floating." When 
observations are being taken it is very essential that the loaded 

platform be given, 
preferably by hand, a 
slight rotary motion 
to reduce to a mini- 
mum the friction of 
the piston in its cylin- 
der. 

Suggested Proce- 
dure with Dead-weight 
Testers. The accura- 
cy of the gage to be 
calibrated is deter- 
mined by subjecting 
it to known pressures 
and noting its error. 
Before the piston has 
-Crosby Dead-weight Gage Tester. been put into place 

the reading of the 
gage, called "zero-reading," should be observed and recorded in a 




16 



POWER PLANT TESTING 



form similar to the one on page 20. Then the pressure should 
be increased 5 pounds per square inch at a time (corresponding 
usually to a weight of 1 pound) up to the limit of the gradu- 
ations on the dial, spinning the piston gently when each reading 
is taken. Commencing then with the highest pressure the 




Fig 22. — Sectional View of a Dead-weight Gage Tester. 



same operation should be repeated by decreasing the pressure 
by the same increments. 1 

1 When the pressure is being decreased the movement of the pointer 
must be always in a counter-clockwise direction just before a reading 
is taken. In other words, if a weight of 2 pounds has been taken from 
the load on the piston when only 1 pound should have been removed 
the pointer will, of course, get below the next point to be calibrated. 
To secure the reading missed it will not be correct to add 1 pound and 



MEASUREMENT OF PRESSURE 



17 



A modification of the dead-weight gage tester is shown in Fig. 
23. This instrument is particularly suited for calibrations at high 
pressures. Its range is from o to 1500 pounds per square inch. 

Any pressure within these limits can be obtained without 
shifting heavy 
weights. Read- 
ings are taken 
when the scale 
beam is balanced. 
The hand wheel 
A is used to regu- 
late the fluid pres- 
sure by means of 
a plunger as in the 
apparatus shown 
in Figs. 21 and 22. 
The other hand- 
wheel B shown in 
the figure must 
be kept rotating 
when observa- 
tions are taken. 
The slight jar- 
ring of the parts 
due to its rota- 
tion serves to 
make the" friction 
as small as possible. For still higher pressures up to 12,000 
pounds per square inch, a heavy stationary type shown in 
Fig. 24 can be used. 




Fig. 23. — Crosby Portable Fluid Pressure Scales. 



take the reading, because the friction and lost motion will now be in the 
same direction as with increasing pressures; and to overcome this diffi- 
culty the pressure must be increased again to a value higher than that 
for which the reading is to be taken. For the purpose of increasing the 
weight it is not necessary to put on more weights, as additional load in 
such cases can be put on by the pressure of the hand. 

The same precautions apply with even greater force to calibrations 
made with test gages or with a mercury column. With either of these 
instruments discrepancies may occur with increasing or decreasing pres- 
sures. In fact the only certain way to get satisfactory results with these 
instruments is to keep the pointer of the gage or the mercury column, as 
the case may be, moving continually in the same direction. 



18 



POWER PLANT TESTING 



Calibration of Gages with Mercury Columns. The ultimate 
standard for the determination of reasonably high pressures 
is the mercury column, but the apparatus required is so com- 
plicated and occupies so much space that this method is suit- 
able only for use in laboratories where it will have the attention 
of skilled observers. 

For the purpose of calibrating steam gages mercury columns 
have been fitted up in a variety of ways. Simplest of these 

is the method of connect- 
ing, the gage to be tested 
by means of a short tube 
to a " closed " mercury 
well into the top of which 
a long glass tube has been 
inserted. The pressure can 
then be increased either 
by displacing some of the 
mercury in the well by 
means of the plunger in 
the mercury pump shown 
atth e right-hand side of 
Fig. 25, and forcing it up 
into the glass tube, or else 
by pouring mercury into 
the tube from the top as 
must be done in the ap- 
paratus shown in Fig. 26. 
Zero pressure for compari- 
son is to be taken on the 
column at the same level as the center of the gage. Beginning 
then with 5 pounds per square inch pressure on the gage observe 
the corresponding height of the mercury column and its tem- 
perature, and then continue the observations, first increasing 
the pressure and then decreasing by increments of 5 pounds, 
as indicated by the gage. Equivalent units for calibration 
can be computed from the height of the mercury column, since 
1 inch of mercury at 70 degrees Fahrenheit is equivalent to 
a pressure of .4906 pound per square inch. 

When using a mercury-testing apparatus it is necessary 
to observe the temperature near the mercury column in the 




Fig. 24. 



-Fluid Pressure Scales for High 
Pressures. 



MEASUREMENT OF PRESSURE 



1!) 



room in which the work is being done, so that the observed 
height of the mercury column can be corrected to a tempera- 
ture at which the relation between pressure in pounds per 
square inch and height is known. The coefficient of cubical 
expansion of mercury is not constant, as 
will be observed from the following table : 



Temp. Deg. 


Coefficient of 


Fahr. 


Cubical Expansion 


3 2 


.0000998 


5° 


.0001000 


70 


.0001002 


90 


.0001004 


1 10 


.0001007 





Fig. 25. — Standard Mercury Column and Fig. 26. — Simple Open 
Hand Pump. Mercury Column. 



20 



POWER PLANT TESTING 



For very accurate work allowance must be made for the 
expansion of the graduated scale. Coefficients of expansion 
of metals are given in the Appendix. 

Instead of connecting the gage directly to the mercury well, 
it is sometimes connected to one end of a steam drum and the 
mercury column is connected to the other. The increments 
of pressure are then obtained by increasing or decreasing the 
steam pressure in the drum. 

Observations taken in the calibration of a steam gage 
should be recorded and the computed errors tabulated in a 
form similar to the following: 

CALIBRATION OF PRESSURE GAGE. COMPARISON WITH 
GAGE TESTER 



Date Observers 

Maker of gage Maker's No 

Laboratory No Limits of Graduation. 



No. 


Weight 


Gage Readings. Lbs. per sq. in. 


Actual 


Mean Error 




of 


on 
Tester 




Pressure. 
Lbs. per 


of gage. 
Lbs. per 


Remarks 


Reading. 












Lbs. 


Up. 


Down. 


Mean. 


sq.in. 


sq.in. 





















The error of the gage is determined by the comparison of 

the mean of the up and down readings with the actual pressure- 
Curves. From the data tabulated two curves are usually 

plotted : 

i . Mean gage readings (abscissas) and actual pressures (ordi- 

nates). Use a large sheet of coordinate paper for this curve. 
2 . Error Curve : Mean Gage Readings (abscissas) and mean 

corrections, positive and negative (ordinates). See curve in 



MEASUREMENT OF PRESSURE 



21 



Fig. 27. Error curves should have the points, if very irregular, 
connected by a broken line rather than by a " fair " or average 
curve through them. Never, however, try to draw an irregular 
curve through each of a number of scattered points when the 
points are supposed to follow a definite relation between the 
coordinates selected. A " fair " curve should then be drawn 
between the irregular points. 

Calibration of Vacuum and Low-pressure Gages. A vacuum 
gage is usually calibrated by connecting it to one end of a 
U-shaped glass tube of which both legs are about 30 inches 



+4 
a 

w 

+2 
& 

sr ° 


-4 


LlHJ' 

■A 


1 

Tf-T] 

T 


111 111 111 111 llfttii 

iififii'iif 

iPiif 


ffl 

f , jif-,; 


1 

-\ 

- : - -:■}•!- 


j i : : 
EH: 
f-rH: 

J :: : 

TT 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 
Mean Gage Readings. Lbs. per Sq. In. 

Fig. 27. — Typical Error Curve for a Pressure Gage. 

long and are filled to about half their length with mercury. 
The U-tube and gage are then connected to the receiver of an 
air pump or else to an aspirator or ejector operated by water 
or steam pressure, such as chemists use for vacuum filtering. 
The aspirator is really the more convenient instrument to use. 
If the readings of the vacuum gage are correct, they will corre- 
spond exactly with the difference in the level of the mercury 
in the two legs of the U-tube. 

In case a condensing engine is operating when the calibra- 
tion of the vacuum gage is to be made, both the gage and the 
glass U-tube may be connected to the condenser. A compari- 
son of the readings taken will show, under the best possible 



22 POWER PLANT TESTING 

conditions, the absolute errors of the gage. A suitable scale 
about 30 inches long and accurately graduated should of course 
be provided and placed between the two legs of the U-tube. 

An apparatus consisting of an air-pump designed for a high 
vacuum and a mercury column is. illustrated in Fig. 28. It is 
a very convenient means for testing vacuum gages. 




Fig. 28. — Air Pump and Mercury Columns for Testing Vacuum 

A low-pressure gage with a scale from say o to 15 pounds 
per square inch is very easily and accurately calibrated by 
using the same glass U-tube mentioned for the calibration of 
the vacuum gage with air pressure, preferably, or with steam 
pressure. Otherwise the method for calibration is the same as 
for a vacuum gage, except that inches of pressure instead of 
inches of vacuum are observed. 



MEASUREMENT OF PRESSURE 



2:} 




Draft Gages. Many engineers use an ordinary glass U-tube 
manometer (Fig. 29) filled with water for measuring small 
pressures like that due to the draft in a 
chimney or that produced in air-ducts by 
ventilating fans or blowers. For such obser- 
vations in many cases, however, greater 
accuracy is desired than can be secured by 
the use of the ordinary U-tube and a special 
form of manometer is used in which the dis- 
tance moved by the surface of the liquid in 
the tube is greater than the vertical change 
of level. Fig. 30 illustrates a simple device 
of this kind. It consists of a bottle B, filled 
with water, having a suitable opening at the 
bottom to which by means of a short rubber 
tube the inclined glass tube CD is attached. 
At the upper end of this tube a piece of 
rubber tubing T is shown and is intended 
to be connected to the chimney, duct, or 
flue in which the pressure is to be obtained. 
A scale placed behind the inclined tube CD 
should be graduated so that when the spirit 
level L is adjusted, vertical differences in 
level in the bottle will be indicated by the 
scale. Then differences in the readings of, the scale will give 
directly the difference in pressure in inches of water just as 
with an ordinary U-tube. 



Fig. 20. — Simple 
U-tube Draft Gage. 





B 


c rnT 




~-~AD^_^X/ 


E3^rE==E=5 


nm 



Fig. 30. — Inclined Tube Draft Gage. 



Very accurate draft gages of this type known as Ellison's, 
are shown in Figs. 31 and 32. The inclination of the tube in 
these instruments is usually about 1 to 10. Instead of water 
a very light oil is used to fill the tube. It is claimed that this 



21 



POWER PLANT TESTING 



oil has the advantages of having less capillarity than water 
and also, being lighter, permits the use of a longer scale for a 
given difference in level. Graduations on these instruments 
which are sold commercially 1 are, however, always made to 




Fig. 



-Ellison's Improved Draft Gage. 



read equivalent inches of water. These draft gages are also often 
used for measuring small differences of pressure. For example, 
if there are two vessels containing gases at different pressures 
and one is connected to the left-hand side and the other to the 




Fig. 32. — Ellison's Differential-direct Draft Gage for High Drafts. 

right-hand side of the gage, it will indicate the difference in 
pressure. 

When calibrating gages it is worth while to notice that 
when instruments are to be used to observe practically con- 
stant values it is necessary to calibrate them only near the 
values to be observed. 

1 American Steam Gage and Valve Mfg. Co., Boston and Chicago. 



CHAPTER II 
MEASUREMENT OF TEMPERATURE 

Mercurial Thermometers. Temperatures less than about 
500 degrees Fahrenheit are usually measured by means of 
mercurial thermometers, depending for their action on the 
expansion of mercury in a glass bulb and a graduated capil- 
lary tube. 1 

Whenever mercurial thermometers are used for any work 
where reasonable accuracy is expected they should be care- 
fully calibrated before the test is made ; and . after the test 
the calibration should be at least roughly checked to be sure 
that the zero of the thermometer has not changed. Too 
often it happens in practice when tests are being made, as 
for example of a boiler or of a steam turbine, that in some 
way a thermometer not previously calibrated has been used, 
and before the end of the test is broken. It is then too late 
to get a calibration and sometimes very important results of 
tests are made doubtful because of such negligence. 

Calibrations of thermometers of all kinds must be made 
often because there is always the possibility that a little of 
the mercury has become detached from the column and remains 
unobserved either on the sides or at the top of the capillary 
tube. In all glass thermometers there is always taking place 
with use and time a gradual and permanent change in the 

1 The best thermometers for ordinary engineering work are those 
having graduations etched on the tube. The only difficulty with this 
method is that after considerable, use the ink originally in the etched 
markings disappears and it becomes difficult to read the scale. When 
this happens a thick paint made of lampblack and shellac or printer's 
ink can be rubbed over the etched scale, and when this paint is rubbed 
off after a few minutes, there will be enough of it left in the etchings 
to make the scale as legible as when new. A crayon or pencil of soft 
greasy graphite like those used by glaziers for marking glass or by ship- 
pers for marking cases is a satisfactory substitute for the paint, although 
it is not so permanent. 

25 



26 POWER PLANT TESTING 

volume of the bulb, more in new thermometers than in old 
ones, altering the zero point, and of course, also the true 
values for all the graduations. 

Alcohol Thermometers. For the measurement of tempera- 
tures much below zero Fahrenheit thermometers filled with 
mercury are not satisfactory, and alcohol or " spirits of wine " 
is used. These liquids, on the other hand, are not suited on 
account of their high vapor tensions for high temperatures. 

Conversion of Temperatures and Heat Units. Tempera- 
tures in Centegrade degrees are converted into Fahrenheit by 
multiplying by §■ and adding 32. Kilogram-calories multiplied 
by 3.968 give the equivalent British thermal units (B.T.U.), 
and kilogranncalories per kilogram X1.8 give British thermal 
units per pound. A " small " or gram calorie is one-thou- 
sandth as large as a kilogram-calorie. 

Calibration of Thermometers. Tests to determine the accu- 
racy of thermometers are made by subjecting them to known 
temperatures and noting the errors. This is done usually in 
one of two ways: 

1. By comparison with a so-called " standard " thermom- 
eter known to be accurate. 

2. By comparison with temperatures corresponding to 
steam pressures. 

Since the second method is not applicable for temperatures 
below the boiling point of water, it is not often used for 
temperatures below 212 degrees Fahrenheit. For "low-read- 
ing " thermometers, therefore, the first method is generally 
used. 

Calibration by Comparison with a Standard Thermometer. 
For low-temperature calibrations, the thermometers to be 
tested are usually suspended together with a " standard " 
thermometer of which the errors are known in a water bath 
arranged so that the temperature can be varied. This bath 
may consist simply of a vessel provided with a coil of pipe 
through which steam can be circulated, and has also a suitable 
stirring device. If the water is kept well stirred in such an 
apparatus a uniform temperature can be maintained and three 
or four thermometers can be calibrated at the same time. 

Fig. 33 illustrates diagrammatically a very simple apparatus 
of this kind, except that the water bath is heated by discharg- 



MEASUREMENT OF TEMPERATURE 



27 



ing steam directly into the water. This arrangement permits 
changing the temperature more rapidly than with the coil of 
pipe mentioned above. 

" Standard " thermometers for comparison should be pref- 
erably those which have been calibrated at standardizing 
laboratories such as at the U. S. Bureau of Standards at Wash- 
ington, D. C, at the Reichsanstat at Berlin, Germany, or at 
the Royal Physical Testing Laboratories in London, England. 



Thermometers 



a 



t — Paddles 



% 



Fig. 33. — Apparatus for Calibration of Thermometers at Temperatures 
Less than the Boiling-point of Water. 



The steam laboratories of nearly all technical colleges have 
sets of standard thermometers suitable for determining the 
errors of good thermometers to be used as " secondary " 
standards. 

When the method of comparison with a " standard " ther- 
mometer is to be used for temperatures higher than are obtain- 
able with the apparatus shown in Fig. 33, the " standard " 
thermometer and the other thermometers to be calibrated are 
placed in adjacent cups or wells of the same depth inserted in 
a suitable cylindrical drum with pipe connections permitting 



28 



POWER PLANT TESTING 



a flow of steam through it. The thermometer cups or wells 
should be filled with cylinder oil or, preferably, for high tem- 
peratures, with mercury. 1 Temperature is varied by throttling 
with the valves on either or both the steam inlet and discharge 
pipes. Usually the necessary adjustment is made more easily 
by manipulating the discharge valve rather than the inlet. At 
least five minutes should be allowed after the valves have been 
adjusted for the mercury in the thermometers to come to rest 
before readings for comparison are taken. Readings of both the 
standard and the thermometer being calibrated must be taken 
as nearly as possible at the same time, and the thermometers 
should be lifted from their cups when necessary just enough 
to bring the mercury into view. Observations should be taken 
as quickly as possible to avoid errors due to cooling and should 
be made with approximately the same increments. 1 

A record of the observations should be made in the form 
given below. 



CALIBRATION OF THERMOMETER 



By comparison with " STANDARD " 

Date Observers 

Standard: Thermometer Tested: 

No. or distinguishing mark No. or distinguishing mark. 

Range of scale Range of scale. . . 





Standard 
Thermometer. 


True 
Temper- 
ature. 

o p 


Thermometer 
Tested. 




No. 


Reading, 
o p _ 


Known 
Error. 

op 


Reading. 

o p_ 


Error. 

(+ or -) 

o p 


Remarks. 

















1 If oil is used in thermometer cups, precautions should be taken 
that the oil is absolutely free from the presence of water and that 
there is no water in the cups. If water is allowed to accumulate there 



MEASUREMENT OF TEMPERATURE 29 

Calibration of Thermometers by Comparison with Tempera- 
tures Corresponding to Steam Pressures. There is a definite 
temperature of saturated steam corresponding to every pressure. 
If, then, the pressure is known, the temperature corresponding 
can be obtained from " Tables of the Properties of Saturated 
Steam." * 

Thermometers to be calibrated are placed in adjacent cups 
or wells of the same depth inserted in a cylindrical steam drum 
and filled with cylinder oil or mercury. Pipe connections must 
be provided for the attachment of an accurately calibrated 
steam gage and valves are needed at the ends of the drum for 
regulating the flow of steam through it. Except for the ad- 
dition of the gage the apparatus is the same as that used for 
the calibration of thermometers at high temperatures explained 
in the preceding paragraphs, and the manipulation of the ap- 
paratus as well as the precautions to be observed are also the 
same except that the pressure registered by the gage is recorded 
instead of the temperature indicated by the " standard " ther- 
mometer. 

If there is any possibility that the steam supplied to the 
drum is superheated, then it is necessary to provide a water- 
jacket around the steam pipe large enough to make the steam 
at least dry saturated or preferably slightly wet. Another 
device often used to change superheated steam to the saturated 
condition is illustrated in Fig. 34. In this apparatus the steam 
passes down through the vertical supply pipe S closed at the lower 
end and escapes from perforations near the bottom to bubble 
up through the water contained in the chamber A and is carried 
away in the pipe D. In this way the steam can be made to 
lose enough heat to the water to reduce the superheat. A 
gage glass G at the side of the drum is serviceable for showing 
the level of the water. 



may be a slight explosion, sometimes strong enough, however, to throw 
the thermometer out of the cup. 

Thermometers used for measuring high temperatures should be 
protected from contact with the metal of the cups by wrapping the 
stems at the mouth of the cup with cotton waste, or, preferably, with 
rings of cork. 

1 Marks and Davis' Steam Tables and Diagrams or Peabody's Steam 
and Entropy Tables (revised 1909) are recommended. 



30 



POWER PLANT TESTING 



A most excellent method for making calibrations of ther- 
mometers by means of a steam drum is a combination of the 
last two methods described. That is, the corrections are calcu- 
lated from the temperature corresponding to the corrected 

gage pressure; but at the same 
H — |j~"X time are checked by comparison 

1} > V with a •' ' standard ' ' thermometer. 

In all experimental work in 
engineering such methods of 
checking results cannot be too 
highly commended. Checking 
not only assists in the elimina- 
tion of errors of observation as 
well as in calculations, but for 
the engineer it is his key to 
success. 1 

Observations should be tabu- 
lated in the form given on page 
31. The column under the head- 
ing " Standard Thermometer" 
is to be left blank, of course, 
when only the steam gage is 
used for the calibration. To 
obtain the absolute pressure 
the barometric pressure must 
be observed during the cali- 
bration. 

Curves. 1. Plot a curve 
for each thermometer showing 
observed temperatures of the thermometer tested (abscissas) 
and the corresponding "true" or "standard" temperatures 
(ordinates). This curve is of no value, however, unless a 
reasonably large scale is used. 

2. Plot an error curve, taking observed temperatures of 
thermometer tested for abscissas and " errors " for ordinates. 
Compare with Fig. 27. 




Fig. 34. — Apparatus to Reduce 
the Superheat in Steam. 



1 The plotting of curves is still another means which the engineer 
uses continually for checking his calibrations, his tests, and his conclu- 
sions. It has been well said that " the physician buries his mistakes 
but that the mistakes of the engineer bury him." 



MEASUREMENT OF TEMPERATURE 



31 



CALIBRATION OF THERMOMETER BY COMPARISON WITH 
TEMPERATURES CORRESPONDING TO STEAM PRESSURES 

Record. : 

i. Date and names of observers 

2. No. and type of gage 

3. No. of standard thermometer . .' ; 

4. Identification of thermometer tested 

5. Limits of graduation of both '. 

6. Barometer reading ins. mercury 



1 


2 3 


4 


S 


6 


7 


8 


9 


10 






_£ 

a 


Observed 

Temperatures 

°F. 


Pressures 
Lbs. per Sq.In. 


| 

•V 
C 

00 

a 


a* 

a ^ 

2 H 

H 


■d 

1; 

a - g 

:°t 




•a 


i 

^ B 
* ir! 

f H 


<u 

6 -d 

<u 

6 3 
H 


.5 


pq 


M 

O « 

H .5 



+ 

<; 


Remarks. 

























Experience has shown that certain types of thermometer 
cups or wells for use in pipes give more satisfactory results than 
others. The thermometer cup must be long enough to enter 
well into the pipe so that the flow of fluid, through it will be 
around the well. In other words it should, be located so that 
it will be in the "main stream" and not in such a position 
where only eddies touch it. A well-designed thermometer cup 
is illustrated in Fig. 35. 

Correction for " Stem Exposure " of Mercury Thermom- 
eters. When a considerable portion of the mercury column 
of a thermometer measuring high temperatures is exposed to 
the air, a correction K must be added to the readings to ob- 



32 



POWER PLANT TESTING 



tain the true temperature. If t is the observed reading, D 
is the number of degrees Fahrenheit on the scale from the 
surface of the oil or mercury in the thermometer cup to the 




The Right Way. The Wrong Way. 

Fig. 3 5- — Typical Thermometer Wells — " Good and Bad." 

end of the mercury column, and t' is the temperature of the 
air surrounding the thermometer stem, then 



K=.ooo,o88D(t-t'). 



. . • • d) 

This equation, it will be observed, includes three factors: coef- 
ficient of expansion, length, and temperature difference. The 



MEASUREMENT OF TEMPERATURE 



33 



coefficient of expansion given in the equation is the difference 
between the volumetric coefficient of expansion of mercury 
(.000,100) 1 and the linear coefficient (.000,012) of the kind 
of glass ordinarily used for thermometers. 




Fig. 36. — Typical Recording Thomometer with Flexible Tube. 

In practice for carefully conducted tests of engines or tur- 
bines operating with superheated steam the above correction 



1 An average value of the volumetric coefficient is used here. A 
table sho-wing the variation of this coefficient is given on page 19. 



34 POWER PLANT TESTING 

should always be added to the thermometer readings to obtain 




imuiuimmuuuwumuui 



Fig. 37. — " Sensitive " Bulb for a Recording Thermometer, 
the correct temperature and superheat. In steam turbine 
tests, when a high degree of superheat is used, this correction 

is often as much as from 
5 to 10 degrees Fahren- 
heit. 

Recording Thermome- 
ters. Recently instru- 
ments for recording auto- 
matically low as well as 
high temperatures have 
been very satisfactorily 
developed. A typical ex- 
ample is shown in Fig. 
36. It consists of a 
sensitive bulb (Fig. 37) 
suitable for being inserted 
into a pipe fitting and is 
attached by a capillary 
connecting tube to the 
recording instrument. 
The sensitive bulb and 
capillary tube are filled 
with either alcohol or 
ether, which is sealed 
in the bulb and tube 
under pressure. The in- 
strument is operated by the expansion of the vapor of these 




Fig. 



-Mechanism of a Recording 

Thermometer. 



MEASUREMENT OF TEMPERATURE 35 

liquids. One of these instruments is shown in Fig. 38 
with the cover removed so that the mechanism can be seen. 
It is exactly the same as that of a recording pressure gage (see 
page 10). 

In general appearance these recording thermometers are 
like the recording pressure gages now in general use, and in 




Fig. 39. — Recording Thermometer, Short Bulb Type. 

other respects as regards the recording mechanism and clock- 
work they are also practically the same. Movement of the 
recording pencil proportional to the temperature is secured 
in most instruments of this kind by the expansion of ether or 
mercury m the "sensitive" bulb inserted usually by screw threads 
in the pipe or chimney where the temperature is to be obtained. 
Some of these recording instruments, Fig. 39, have a short rigid 



36 



POWER PLANT TESTING 



connection between the bulb and the recording mechanism, 
making it necessary to locate the instrument always immediately 
adjacent to the bulb. In Fig. 36 there is a flexible connection 
of capillary tubing attached to bulb permitting the setting 
up of the instrument on a wall near by. This capillary tube 
must, however, be handled very carefully to prevent causing a 
serious leak, making the instrument useless. 

Pyrometers. Temperatures over 600 degrees Fahrenheit 
are usually measured by instruments known as pyrometers. 
Various types are in use particularly for the measurement of 

temperatures in flues and chim- 
neys of boiler plants. The 
thermo-electric pyrometer is 
probably the one most com- 
monly used in modern plants 
and is doubtless the most reliable . 
One of the best -known makes is 
illustrated in Fig. 40. It consists 
of a twisted joint formed of 
wires of two different metals 
having such thermo-electric prop- 
erties that when joined they 
generate an electric current 
capable of deflecting a sensitive 
galvanometer. When, there- 
fore, this joint or " couple " is 
heated the electric current gen- 
erated produces a deflection of 
the needle of the galvanometer in 
proportion to the temperature. 
The scale of the instrument is generally graduated to read 
directly in degrees of temperature. For instruments reading 
up to about 1500 degrees Fahrenheit the "couple" consists 
of a wire of nickel for the positive element and an alloy of 
nickel and chromium for the negative element, while if the 
thermo-electric joint is made of one wire of pure platinum and 
another of an alloy of platinum and about ten per cent of rho- 
dium or of iridium, temperatures nearly as high as the melting 
point of platinum, or nearly 3500 degrees Fahrenheit, can be 
measured, although 3000 degrees Fahrenheit is considered the 




Fig. 40. — Thermo-Electric 
Pyrometer. 



MEASUREMENT OF TEMPERATURE 



37 




Le Ch atelier Pyrometer. 



safe limit. This pyrometer with a platinum "couple " is known 

as the Le Chatelier (Fig. 41). 

Electric Resistance Pyrometers like the one illustrated 

Fig. 42 are sometimes 

preferred when a very 

sensitive instrument is 

desired. The "heating" 

element consists of a coil 

of very fine platinum wire 

wound on a mica frame. 

The current from one 

electric battery passes 

through this wire, and 

the current from another 

battery passes through 

the coil of " resistance " 

wire in the cover of the 

box. When the two cir- 
cuits are connected so 

that the electromotive forces of the two batteries are opposed, 

the resistance in the cover is adjusted by means of a connec- 
tion on a stylus so that 
there is no current passing 
through a telephone or a 
galvanometer placed at the 
junction of the two cir- 
cuits. For making obser- 
vations this stylus is moved 
along the " scale " wire in 
the cover to a point where 
the humming noise due 
to the electric current 
ceases. The temperature 
can then be read on the 
scale opposite the position 
of the stylus. 

By means of a switch- 
board any number of ' ' heat- 
ing " elements can be connected to the same indicator box, 

which may be located at any distance from the source of heat. 




Electric Resistance Pyrometer. 



POWER PLANT TESTING 



Mechanical Pyrometers consist of two metals having dif- 
ferent rates of expansion, such as copper and iron or graphite 
and iron. By means of levers and gears the expansion is made 
to rotate a needle over a dial graduated in degrees. One of 
these instruments is illustrated in Fig. 43. It can be used 
safely to 1 500 degrees Fahrenheit. 

Calibrations of " Indicating " Pyrometers such as the thermo- 
electric and metallic are best made by comparison with a special 
standard pyrometer of which the error 
is known and which is used only for 
standardizing work. The couple to be 
calibrated and the standard should be 
fastened together closely with only a 
sheet of asbestos between them. The 
two couples thus bound together should 
be put into an electric furnace in which 
the temperature can be controlled and 
raised very slowly. Then at different 
points in the scale, at intervals of 
about fifteen minutes, readings for com- 
parison can be taken. If a standard 
pyrometer is not available a calibration 
can be made by comparison in a furnace 
of constant temperature with a good 
mercury thermometer. Such thermom- 
eters in which the capillary tube con- 
tains rarefied nitrogen above the mercury 
can be obtained to measure tempera- 
tures with a fair degree of accuracy, 
when new, up to 1000 degrees Fahrenheit. 

Recording Pyrometers are most frequently of the type of 
recording thermometers illustrated and described on pages 33-35. 
Such instruments can be constructed, when the sensitive bulb 
is filled with a gas instead of a liquid, to register accurately 
temperatures as high as 1 200 degrees Fahrenheit. 

Another type operated by the expansion of the vapor of 
mercury is shown in Fig. 44. This is a combined indicating 
and recording instrument. The sealed tube A is to be inserted 
in the chimney or flue in which the temperature is to be 
observed. 




Fig. 43. — "Mechanical 
Pyrometer. 



MEASUREMENT OF TEMPERATURE 



39 



Optical Pyrometers. For temperatures above 2500 degrees 
Fahrenheit optical pyrometers similar to the one illustrated 
in Figs. 45, 46 and 47 are most suitable. They can also be 
used in many places where is it almost impossible to locate a 
pyrometer of any of the other types. It consists of a cylindrical 
case set upon a tripod. This case contains a concave mirror 
and a lens (or lenses) which when properly adjusted and focused 
on a hot body concentrate the heat rays upon a small thermo- 
electric couple inside the case. Copper wires connect this couple 




Fig. 44. — Combined Indicating and Recording Pyrometer. 



with a very sensitive portable galvanometer (Fig. 46) located 
where it can be read conveniently. The most modern instru- 
ments of this kind are provided with scales indicating directly 
degrees of temperature. Fig. 47 shows a section of the telescope 
used in connection with this pyrometer. The concave mirror 
M receives the heat rays and focuses them at F, where a 
small thermo - couple is located. To assist in pointing the 
telescope an eye-piece E is provided through which a reflected 
image of the hot body can be seen. The rack R and the 
pinion P, moved by a thumbscrew outside the case, serve 



40 POWER PLANT TESTING 

for adjusting the focus of the mirror. In the center of the 
field of view, as seen in the eye-piece, the thermo-couple is 
seen as a black spot, and this must be overlapped on all 




Fig. 45. — An Optical (Radiation) Pyrometer in Use. 

sides by the image of the hot body to obtain the correct 
temperature. It is interesting to observe that the distance of 
the telescope from the source of heat does not affect the reading 
of the instrument. When the telescope gets nearer the hot. 
body the mirror M receives of course more heat, but at the same 



MEASUREMENT OF TEMPERATURE 



41 




Fig. 46. — Sensitive Galvanometer 
Fery Radiation Pyrometer. 



time this greater amount of heat is distributed over a larger 
image and the intensity of the heat remains the same. 

Optical pyrometers are 
invaluable for determining 
the temperatures of the 
various parts of a furnace, 
of the walls of the setting 
of a steam boiler, of various 
portions of a bed of coals, 
etc. 

Another type of optical 
pyrometer, based in prin- 
ciple upon the measure- 
ment of the brightness of 
the hot body by compari- 
son with a standard lamp 
is shown in Fig. 48. In 
order to use this instru- 
ment, known as Wanner's, 
the incandescent (osmium filament) lamp must first be stan- 
dardized by comparison with an amylacetate oil lamp of 

constant candle power. 
Then after standardizing 
it is only necessary to 
focus the instrument upon 
the hot body to be meas- 
ured and the temperature 
is read directly on the 
graduated scale at the 
eye-piece. 

Calorimetric Pyrometers. 
If the specific heat and 
weight of a body are known, 
its temperature can be ob- 
tained by observing the rise 
in temperature of a known 
quantity of water into 
which the body is thrown. 
More in detail the method consists in the determination 
of temperature by putting a ball of metal or other refractory 




Fig. 



17. — Telescope of Fery Radiation 
Pyrometer. 



42 



POWER PLANT TESTING 



material into the medium of which the temperature is to be 
measured. When the ball has become heated uniformly 
throughout its mass to the temperature of the medium it is 
transferred quickly to a cup heavily jacketed with non-con- 
ducting material in which there is a known weight of water at 
a known temperature. Copper, wrought-iron and fire-clay 
are suitable materials. Specific heats of these materials at 
about 500 degrees Fahrenheit are respectively .097, .110 and 
.180. Since metals are readily attacked by furnace gases they 
should be protected when used in this way in a crucible of 
refractory material. 




Fig. 48. — Wanner Optical Pyrometer in Position for Standardizing. 

This method is often very serviceable in places or at times 
when accurate pyrometers are not available. On account of 
the " personal " error liable to enter, such determinations 
should be repeated several times to check the results. Calcu- 
lations required are as follows. 1 

Let Wi = weight of the ball, pounds. 

W2 = weight of the cup (only the " inner ' ' vessel) , 2 pounds. 
W3 = weight of the water in the cup, pounds, 
ti = initial temperature of water, degrees Fahr. 
t 2 = final temperature of the water, " " 

1 A more complete description of calorimetric pyrometers and the 
precautions to be observed for accuracy will be found in Proceedings 
American Society of Mechanical Engineers, vol. VI, page 712. 

2 It would be more accurate, of course, to use in the calculation the 
water equivalent of the whole vessel, as is done in coal calorimetry. See 
page 162. Units given are in pounds and degrees Fahrenheit, but other 
units, provided they are corresponding, can be used in the equation given. 



MEASUREMENT OF TEMPERATURE 



43 



Let t = 
Then 



initial temperature of the ball, degrees Fahr. 
specific heat of the ball, 
specific heat of the cup. 

WiSi(to-t2) = (W2S 2 +W 3 )(t2-ti), 



to = 



(W2S 2 +W 3 )(t 2 -ti) 
W1S1 



+ t 2 . 



(2) 



Seger Pyrometer Cones. For many purposes when a pyrom- 
eter cannot be well placed fusible Seger cones are used. Such 
cones are made of several different oxides mixed in a manner 
to give a definitely known melting point for each one. The 
melting points range from 590 degrees to 1850 degrees Centi- 
grade by steps of from 20 to 30 degrees, each having a stand- 
ard number. These cones are carefully graded, so that if one 




*&&?&y&^!-#*&'ti'>- ':- ••.". .'■' ': >:-< 



Fig. 49. — Seger Cones after Use. 

has had some experience with them, temperatures can be 
estimated to about the nearest ten degrees in Centigrade. Four 
of these cones are shown in Fig. 49. 

When a series of cones is placed in a furnace the one having 
the lowest melting point begins to turn over first. The tem- 
perature corresponding to the cone number is reached when 
the tip of the cone has bent over and just touches the surface 
on which it is standing. Hence the highest temperature reached 
when the cones shown in the illustration were used was about 
half way between that corresponding to each of the two middle 
cones. According to the numbers on the cones the temperature, 
as given by the table on page 45, was between 830 and 860 de- 
grees Centigrade. The greatest disadvantage with this system is 
that there is no way of observing a decrease in the temperature, 
or, in other words, only the maximum temperature is recorded. 



44 



POWER PLANT TESTING 



Two types of mercury thermometers protected by heavy 
metal cases are illustrated by Figs. 50 and 51. It will be 
observed that a very satisfactory thermometer cup is a part 
of the casing. The one shown in Fig. 51 has graduations for 
reading both temperatures and pressures. A thermometer of 
this type is particularly useful in pipes carrying hot boiler 
feed-water. When the temperature is above 212 degrees 



#51* 



Fig. 50. — Combined Thermometer Fig. 51. — Combined Thermometer 
Cap and Protective Casing. and Pressure Gage for Boiler 

Feed-water Pipes. 

Fahrenheit the thermometer will indicate that the water is 
being heated at a pressure higher than atmospheric. For 
water heated in closed vessels or pipes there is for every 
temperature a corresponding pressure as given in tables of 
the properties of saturated steam. 1 

1 Short and very much abbreviated tables of the properties of 
saturated steam are given in the Appendix. See also references in foot- 
note on page 29. 



MEASUREMENT OF TEMPERATURE 



45 



The following table gives the temperatures, in degrees Centi- 
grade, at which the Seger cones will begin to melt : 



Seger 


Temp. 


Seger 


Temp. 


Seger 


Temp. 


Cone No. 


Deg. C. 


Cone No. 


Deg. C. 


Cone No. 


Deg. C. 


022 


59° 


04 


1070 


I 5 


I430 


021 


620 


03 


1090 


16 


145° 


020 


650 


02 


1 no 


J 7 


1470 


019 


680 


01 


1130 


18 


1490 


018 


710 


r 


1150 


19 


1510 


017 


740 


2 


1170 


20 


153° 


016 


770 


3 


1190 






OI5 


800 


4 


1210 


26 


1650 


014 


830 


5 


1230 


27 


1670 


013 


860 


6 


1250 


28 


1690 


012 


890 


7 


1270 


29 


1710 


on 


920 


8 


1290 


3° 


!73° 


OIO 


95° 


9 


1310 


3 1 


i75o 


09 


970 


10 


1 33° 


3 2 


1770 


08 


990 


11 


!35° 


33 


1790 


07 


IOIO 


12 


1 37° 


34 


1810 


06 


1030 


13 


1390 


35 


1830 


°5 


1050 


14 


1410 


36 


1850 



CHAPTER III 

DETERMINATION OF THE MOISTURE IN STEAM 

Unless the steam used in the power plant is superheated 
it is said to, be either dry or wet, depending on whether or not 
it contains water in suspension. The general types of steam 
calorimeters, used to determine the amount of moisture in the 
steam, may be classified under three heads: 

i . Throttling or superheating calorimeters. 

2. Separating calorimeters. 

3. Condensing calorimeters. 

Throttling or Superheating Calorimeters. The type of 
steam calorimeter used most in engineering practice operates 
by passing a sample of the steam through a very small orifice, 
in which it is superheated by throttling. A very satisfactory 
calorimeter of this kind can be made of pipe fittings as illus- 
trated in Fig. 52. It consists of an orifice O, discharging into 
a chamber C, into which a thermometer, T, is inserted, and 
a mercury manometer is usually attached to the cock V3, for 
observing the pressure in the calorimeter. 

It is most important that all parts of calorimeters of this 
type, as well as the connections leading to the main steam pipe, 
should be very thoroughly lagged by a covering of good insulat- 
ing material. One of the best materials for this use is hair 
felt, and it is particularly well suited for covering the more or 
less temporary pipe fittings, valves, and nipples through which 
steam is brought to the calorimeter. Very many throttling 
calorimeters have been declared useless by engineers and put 
into the scrap heap merely because the small pipes leading 
to the calorimeters were not properly lagged, so that there was 
too much radiation, producing, of course, condensation, so that 
the calorimeter did not get a true sample. It is obvious that if 
the entering steam contains too much moisture the drying 
action due to the throttling in the orifice may not be sufficient 

46 



DETERMINATION OF THE MOISTURE IN STEAM 



47 



to superheat. It may be stated in general that unless there is 
about 5 to 10 degrees Fahrenheit of superheat in the calorim- 
eter, or in other words unless the temperature on the low 
pressure side of the orifice is at least about 5 to 10 degrees 
Fahrenheit higher than that corresponding to the pressure in 




Fig. 52. — A Simple Throttling Steam Calorimeter. 

the calorimeter, there may be some doubt as to the accuracy 
of results. 1 The working limits of throttling calorimeters vary 



1 The same general statement may be made as regards determinations 
of superheat in engine and turbine tests. Experience has shown that 
tests made with from o to 10 degrees Fahrenheit superheat are not 
reliable, and that the steam consumption in many cases is not con- 



48 POWER PLANT TESTING 

with the initial pressure of the steam. For 35 pounds per 
square inch absolute pressure the calorimeter ceases to super- 
heat when the percentage of moisture exceeds about 2 per 
cent; for 150 pounds absolute pressure, when the moisture 
exceeds about 5 per cent; and for 250 pounds absolute pres- 
sure, when it is in excess of about 7 per cent. For any given 
pressure the exact limit varies slightly, however, with the 
pressure in the calorimeter. 

In connection with a report on the standardizing of engine 
tests, the American Society of Mechanical Engineers 1 published 
the following instructions regarding the method to be used 
for obtaining a fair samole of steam from the main pipes. It 
is recommended in this report that the calorimeter shall be 
connected with as short intermediate piping as possible with 
a so-called calorimeter nipple made of ^-inch pipe and long 
enough to extend into the steam pipe to within \ inch of the 
opposite wall. The end of this nipple is to be plugged so that 
the steam must enter through not less than twenty |-inch 
holes drilled around and along its length. None of these holes 
shall be less than \ inch from the inner side of the steam pipe. 
The sample of steam should always be taken from a vertical 
pipe as near as possible to the engine, turbine, or boiler being 
tested. Good examples of calorimeter nipples are illustrated 
in Figs. 54 and 59. 

Never -close and usually do not attempt to adjust the dis- 
charge valve V 2 without first closing the gage cock, V 3 . Unless 
this precaution is taken the pressure may be suddenly increased 
in the chamber C, so that if a manometer is used the mercury 
will be blown out of it, and if, on the other hand, a low- 
pressure steam gage is; used it may be ruined by exposing it 
to a pressure much beyond its scale. 

Usually it is a safe rule to begin to take observations of 
temperature in calorimeters after the thermometer has indi- 
cated a maximum value and has again receded slightly from it. 



sistent when compared with results obtained with wet or more highly 
superheated steam. The errors mentioned, when they occur, are prob- 
ably due to the fact that in steam, indicating less than 10 degrees 
Fahrenheit superheat, water in the liquid state may be taken up in 
"slugs" and carried along without ' being entirely evaporated. 
1 Proceedings American Society of Mechanical Engineers, vol. 21. 



DETERMINATION OF THE MOISTURE IN STEAM 49 

The quality or relative dryness of wet steam is easily cal- 
culated by the following method. Using the symbols, 

pi = steam pressure in main, lbs. per sq.in. abs. 
p 2 = steam pressure in calorimeter, lbs. per sq. in. abs. 
t c = temperature in calorimeter deg. Fahr. 
ri and qj =heat of vaporization, and heat of liquid corresponding 

to pressure pi, B.T.U. 
H 2 and t 2 = total heat (B.T.U.) and temperature (degs. Fahr.) 
corresponding to pressure p 2 . 
C p = specific heat of superheated steam. Assume 0.5 

for low pressures existing in calorimeters. 1 
X!=: initial quality of steam, per cent. 
1 — Xi = initial moisture in steam, per cent. 

Total heat in a pound of wet steam flowing into the orifice is 

xi^+qi, 

and after expansion assuming all the moisture is evaporated, 
the total heat of the same weight of steam is, 

H 2 +c p (t c -t 2 ). 

Then assuming no heat losses and putting for c p its value 0.5 
we have, 

Xiri+q 1 = H 2 +o.5(t c -t 2 ), .... (3) 

Xi = H 2+ o. 5 (t f -t 2 ) -q, 

1*1 

Chart for Moisture Determinations. Using degrees of 
superheat in the calorimeter as abscissas and initial absolute 
steam pressures as ordinates, the diagram in Fig. 53 has been 
constructed. In the calculations it was assumed that the 
pressure in the calorimeter was atmospheric. In cases where 
this condition exists, therefore, after determining the degrees 
of superheat in the calorimeter (t c — 212) and the initial absolute 
pressure pi, the percentage moisture can be read from the curves 
without further calculations. 

1 Average values for the specific heat of superheated steam for any 
i/iiiiperatures are given on page 



50 



POWER PLANT TESTING 



170 
160 

150 


nfflltf "WopHiHiiiflti 1 1 111 1 II 11 1 II II 11 111 1 lilt 

/] ppo?4 | / I / /] 1 / \\\\\ 1 n IflT 




140 

130 

<u 
3 
"o 
Ja 120 

< 


iTJTj / p / o / ' 1 rP^lyfiiTFt 




V 

• no 


^^^^^^^^^^^^P 




0! 
TO 

fc 100 

a 

c 

| 90 


jj^i^lill Ill41i[j^^ 1 [N~~l ' rill ! 

iijf ti Tjl|ljiiiM 


S so 
ft. 

W vo 

60 
50 

40 
SO 
20 


111 'lii^^^^B 

: ^fflffifffffi llifl^TJjffl+f^^ ill 1 1 1 1 1 1 1 1 1 1 1 1 II 1 1 



10 20 30 40 50 60 70 

Superheat in Calorimeter, degrees Pahr. 
Fig. 53. — Chart for Determining Quality of Steam from Pressure and 
Superheat. 



DETERMINATION OF THE MOISTURE IN STEAM 51 

Although all the calculations for drawing this diagram were 
made by assuming atmospheric pressure in the calorimeter, 
the curves in the figure can be used with almost equal accuracy 
for pressures in the calorimeter not exceeding about 5 pounds 
above atmospheric by using the diagram 1 as if the ordinates 
represented the difference in pressure between the two sides 
of the orifice, or in other words the difference in pressure 
between that in the steam pipe leading to the calorimeter and that 
in the calorimeter itself. For example, if the superheat in the 
calorimeter is 40 degrees Fahrenheit, the initial steam pressure 
is 150 pounds per square inch gage and that in the calorimeter is 
5 poundsper square inch gage, then the difference in pressure is 
145 pounds per square inch, which is equivalent, with a barometric 
pressure of 15 pounds per square inch, to 160 pounds per square 
inch absolute pressure. Selecting the abscissa = 40 and the ordi- 
nate =160 the diagram shows that the quality of the steam is 
approximately 96.9 per cent. If with the same data the qual- 
ity X\ is calculated by equation (2), taking again the baro- 
metric pressure to be 15 pounds per square inch absolute, it is 
found to be 96.85 per cent, which for the acciiracy required in 
the ordinary daily power plant calculations is good enough 
agreement, particularly when it is generally conceded by practi- 
cal engineers that it is almost impossible with any of the 
simpler forms of steam sampling devices to obtain samples 
which do not differ as much as J per cent from the 
average. 

When a U-tube manometer is used to determine the pressure 
in a calorimeter of the type illustrated in Fig. 52, this pressure 
can be obtained very accurately and an excellent means is 
provided for calibrating the thermometer in the calorimeter 
just as it is to be used. The calibration would be made, of 
course, by the method of comparing with the temperature 
corresponding to known pressures explained on page 29. In 
order to avoid having superheated steam in the calorimeter 
for this calibration the felt or similar material usually needed 
for covering the valves and nipples between the main steam 
pipe and the calorimeter should be kept saturated with 
cold water. 

1 For the use of this diagram as well as the one in Fig. 55, acknowl- 
edgment is due to Messrs. Schaeffer & Budenberg and R. C. Carpenter. 



52 



POWER PLANT TESTING 



The Barrus Throttling Calorimeter. An important varia- 
tion from the type of throttling calorimeter shown in Fig. 
52 has been introduced quite widely by Mr. George H. 
Barrus. In this apparatus the temperature of the steam ad- 
mitted to the calorimeter is observed instead of the pressure 
and a very free exhaust is provided so that the pressure 
in the calorimeter is atmospheric. This arrangement simplifies 
very much the observations to be taken, as the quality of the 
steam Xi can be calculated by equation (3') by observing only 
the two temperatures ti and t2, taken respectively on the high 
and low pressure sides of the orifice in the calorimeter. This 

calorimeter is illus- 
trated in Fig. 54. 
The two thermom- 
eters required are 
shown in the figure. 
Arrows indicate the 
path of the steam. 1 
The orifice in 
such calorimeters 
is usually made 
about $2 i ncn in 
diameter; and for 
this size of orifice 
the weight of 
steam 2 discharged 
per hour at 175 
pounds per square inch absolute pressure is about 60 pounds. 
It is important that the orifice should always be kept clean, 
because if it becomes obstructed there will be a reduced 
quantity of steam passing through the instrument, making 
the error due to radiation relatively more important. 

In order to free the orifice from dirt or other obstructions 
the connecting pipe to be used for attaching the calorimeter 
to the main steam pipe should be blown out thoroughly with 




Barrus Throttling Steam Calorimeter. 



1 Proceedings American Society of Mechanical Engineers, vol. ii, 
page 790. 

2 Formulas for calculating the exact weight of steam discharged 
from a nozzle are given on pages 148 and 149. In boiler-tests corrections 
should be made for the steam discharged from the steam calorimeters. 



DETERMINATION OF THE MOISTURE IN STEAM 53 

steam before the calorimeter is put in place. The connecting 
pipe and valve should be covered with hair felting not less than 
f inch thick. It is desirable also that there should be no leak 
at any point about the apparatus, either in the stuffing-box 
of the supply valve, the pipe joints, or in the union. 

Fig. 55 is a diagram for the determination of the quality 
of steam which is particularly suitable for use in connection 
with calorimeters of the Barrus type. 

Abscissas in this diagram are temperatures in the calor- 
imeter t 2 , and the ordinates are the initial temperatures ti of 
the steam before expansion in the calorimeter. 

With the help of such a diagram the Barrus calorimeter 
is particularly well suited for use in power plants, where the 
quality of the steam is entered regularly on the log sheets. The 
percentage of moisture is obtained immediately from two 
observations without any calculations. 

Separating Calorimeters. It was explained on page 4S 
that throttling calorimeters cannot be used for the determina- 
tion of the quality of steam when for comparatively low pres- 
sures the moisture is in excess of 2 per cent, and when for 
average boiler pressures in modern engineering practice it 
exceeds 5 per cent. For higher percentages of moisture than 
these low limits separating calorimeters are most generally 
used. In these instruments the water is removed from the 
sample of steam by mechanical separation just as it is done 
in the ordinary steam separator installed in the steam mains of 
a power plant. There is provided, of course, a device for deter- 
mining while the calorimeter is in operation, usually by means 
of a calibrated gage glass, the amount of moisture collected. 
This mechanical separation depends for its action on changing 
very abruptly the direction of flow of wet steam moving with 
considerable velocity. Then since the moisture (water) is 
nearly 300 times as heavy as steam at the usual pressures 
delivered to the engine, the moisture will be deposited because 
of its greater inertia. 

One of the simplest forms of separating calorimeters, made 
of pipe fittings, is shown in Fig. 56. Steam enters at A, passes 
down through the vertical pipe P, plugged at the lower end, 
from which it escapes through a large number of ^-inch holes 
indicated in the figure. In passing through these holes the 



54 



POWER PLANT TESTING 



Tempera 
210 220 230 240 250 


ure in Calorimeter, Degrees Fah 

260 270 280 290 


300 310 320 33 










400 


















390 














"380 












. 370 

1 








S 360 

Q 350 

v 

0) 

J 340 


" 






5 

c 330 

1 


PS' 1 \ YM 

I ' ' i ' ' 1 i 


jfilMMilifiml g 

1 ■Mjijj'jiijijf 




a 320 








£ 310 
o 








.8 

£ 300 
1 

o 290 










I 

g 280 

p. 

i 




Ms 


- |- • 




j^jjIiSg 


H 270 
^ 260 


^^|K|^pi 


IIP 77 




250 
240 














230 
220 










i i-;: iiiiiiifftiilid 





240 250 260 270 280 290 3C 
^Temperature in Calorimeter, Degrees Fahr. 



310 320 330 



Fig. 55. — Chart for Determining Quality of Steam from Temperature 
Observations. 



DETERMINATION OF THE MOISTURE IN STEAM 



55 



direction of flow is changed very abruptly, since the steam, must 
go upward to be discharged at D. Moisture is deposited at 
the bottom of the vessel V, and its volume or weight can be 
determined from the height of the water in the gage glass G 
if the vessel .has been calibrated. Steam discharged from D 
must be condensed and weighed in a pail or barrel contain- 
ing cold water. The percentage of moisture is then found by 
dividing the weight of water collected in the vessel V by the 
sum of the weight of steam con- 
densed and the weight of water 
collected in V. This sum is, of 
course, the weight of the wet steam. 
Radiation Loss. As in all cal- 
orimetry work, in order to obtain 
accurate results there should be a 
covering of hair felt £ inch thick 
over all parts of the apparatus, and 
even then the radiation loss is 
sometimes large enough to make 
corrections necessary. This correc- 
tion is determined by operating two 
calorimeters which are exactly alike 
in construction and in the amount 
of felt covering, in series, and so 
arranged that the second takes the 
discharge of the first. If it is 
known that the discharge from the 
first calorimeter is perfectly dry 
steam 1 then the moisture collected 
in the second calorimeter is the 
condensation due to its own radi- 
ating surface, which should be the same as for the first. 
Calculations for corrected moisture determinations are made 
then by subtracting from the" moisture collected in the first 
instrument the amount condensed in the second. When, of 
course, the. radiation loss has been once determined it is not 
necessary to operate the second calorimeter. 




Fig. 56. — A Simple Separat- 
ing Steam Calorimeter 
Made of Pipe Fittings. 



1 A small throttling calorimeter can be attached to the discharge from 
the first separating calorimeter to determine whether or not the steanT, 
discharged is dry. 



56 



POWER PLANT TESTING 



Carpenter's Separating Calorimeter. Fig. 57 illustrates a 
form of separating calorimeter in which the improvement over 
the one shown in Fig. 56 is in the addition of a steam jacketing 
space receiving live steam at the same temperature as the sample. 

Steam is supplied 
through a pipe A, 
discharging into a cup 
B. Here the direction 
of the flow is changed 
through nearly 1 80 
degrees, causing the 
moisture to be thrown 
outward through the 
meshes in the cup into 
the vessel V. The 
dry steam passes 
upward through the 
spaces between the 
webs W, into the 
top of the outside 
jacketing chamber J, 
and is finally dis- 
charged from the 
bottom of this steam 
jacket through the 
nozzle N. This noz- 
zle is considerably 
smaller than any 
other section through 
which the steam flows, 
so that there is no 
appreciable difference 
between the pressures 
in the calorimeter 
proper and the jacket. 
The scale opposite the gage glass G is graduated to show 
in hundredths of a pound at the temperature correspond- 
ing to steam at ordinary working pressures, the variation 
of the level of the water accumulating. A steam pressure 
gage P indicates the pressure in the jacket J, and since the 




-> = Steam. 
Water. 



Fig. 57. — Carpenter Separating Steam 
Calorimeter. 



DETERMINATION OF THE MOISTURE IN STEAM 57 

flow of steam through the nozzle N is roughly proportional 
to the pressure (see page 148), another scale in addition to the 
one reading pressures is provided at the outer edge of the dial. 
A petcock C is used for draining the water from the instrument, 
and by weighing the water collected corresponding to a given 
difference in the level in the gage G, the scale opposite it can 
be readily calibrated. Too much reliance should not be placed 
on the readings for the flow of steam as indicated by the gage, 
P, unless it is frequently calibrated. Usually it is very little 
trouble to connect a tube to the nozzle N, and condense the 
steam discharged in a large pail nearly filled with water. When 
a test for quality is to be made by this method the pail nearly 
filled with cold water is carefully weighed and then at the moment 
when the level of the water in the water gage G has been 
observed the tube attached to the nozzle, N is immediately 
placed under the surface of the water in the pail. The test 
should be stopped before the water gets so hot that some weight 
is lost by " steaming." The gage P is generally calibrated 
to read pounds of steam flowing in ten minutes. For the best 
accuracy it is desirable to use a pail with a tightly fitting cover 
into which a hole just the size of the tube has been cut 

Combined Separating and Throttling Calorimeters. Calor- 
imeters described are effective in removing practically all of 
the moisture in steam when the pressure is not lower than 25 
pounds gage pressure. For lower pressures, particularly around 
atmospheric, recent experiments show that the efficiency of 
such carloimeters is in some cases not more than 80 per cent. 1 
For this reason in the best current practice for determinations 
of moisture in low-pressure steam a throttling calorimeter 
is attached to the discharge of the separating calorimeter. 
Then if the separating calorimeter has been carefully calibrated 
for radiation loss and the steam escaping from the separating 
calorimeter is tested again in a throttling instrument, it is 
possible to make correct determinations for the percentage of 
moisture in the steam of almost any degree of wetness. An 
apparatus of this kind which is reported to have done excellent 

1 Proceedings American Society of Mechanical Engineers, Aug., 19 10, 
page 1 13 2 . The efficiency of the calorimeter is the ratio of the percentage 
of moisture taken out by the separating calorimeter to the total percent- 
age of moisture, 



58 



POWER PLANT TESTING 



service in tests of Very large low-pressure steam turbines, oper- 
ating with the exhaust from reciprocating steam engines in New 
York city, is shown in Fig. 58. The most unique feature of this 
apparatus is the sampling tube. It was found that for this low- 
pressure steam the ordinary sampling tube of perforated pipe 
(see Figs. 54 and 59) did not give a reliable sample. It was also 
found necessary that the sample should be taken from the main 



J4" Mercury 
Column j/ PipeTher 
Oonuectiou / 




Fig. 58. — Stott's Combined Separating and Throttling Steam Calorimeter- 



without changing its direction or velocity until it is actually 
inside the sampling pipe. If the direction of flow of wet steam 
is suddenly changed when entering the sampling nozzle, the 
entrained moisture, because of its greater specific gravity on 
the one hand and the very slight skin friction between it and 
the surrounding dry steam on the other, will cause it to continue 
in its path in a straight line, so that there is a tendency for only 
dry steam to enter the nozzle, Also if the velocity of the steam in 



DETERMINATION OF THE MOISTURE IN STEAM 59 

the sampler is greater than that in the main, there is a tendency 
for the dry steam to " accelerate " into the nozzle, leaving the 
moisture behind. It has been stated that this action has not 
been observed in tests of steam at high pressures, because (i) 
of smaller differences between the specific gravity of high 
pressure steam and water; (2) greater skin friction; (3) the 
highly divided state of the moisture. 1 

As the throttling calorimeter is ordinarily used it would 
have very little, capacity when used with steam pressures only 
a little above atmospheric; but by making it discharge into 
a receiver in which a vacuum of 28 inches was maintained the 
throttling portion of the calorimeter will evaporate 2 to 3 
per cent of moisture. 

The apparatus shown in Fig. 58 consists of the f-inch brass 
nozzle on the sampling tube which is bent to point in the direc- 
tion opposite to that of the flow of the steam. The lip of this 
nozzle is filed to a knife-edge to avoid disturbing the current 
of steam around the mouth of the sampler by eddies and impact 
against a thick lip. This sampling tube is set up so that it ex- 
tends into the main steam pipe \ of the diameter of the pipe, 
where it has been observed to give practically the true average 
flow. When in operation the valve at the sampling tube is 
opened wide and the flow is regulated by means of the lever 
cock between the separating and the throttling calorimeters. 
The necessary throttling action ordinarily produced by an orifice 
is produced by this cock. A vacuum is maintained in the 
throttling portion from which the discharge is carried to a 
small cooling receiver in which the steam is condensed. From 
this receiver it flows to a " volumetric " measuring tank of 
which the top is tightly closed and connected by {-inch pipes 
to the main condenser. A spy-glass shown at the left in the 
figure is useful for proving that the calorimeter is working 
properly. It often happens that when the superheat in the 
calorimeter is less than 5 t'o 8 degrees Fahrenheit there is some 
moisture passing through and the spy-glass will invariably 
show it. As the spy-glass is most conveniently made of f-inch 
gage glass its area is not large enough to carry all the steam, 
and a by-pass connection is arranged as shown. The large size 

1 H. G. Stott, Proceedings American Society of Mechanical Engineers, 
Aug., 1910, 



60 POWER PLANT TESTING 

of the parts is necessary on account of the very large specific 
volume of the low-pressure steam. 

All parts of the apparatus are carefully covered with mag- 
nesia-asbestos covering 2 inches thick. For the normal rate 
of flow for the instrument, the radiation can be made less than 
0.1 per cent. 

Calculation of Percentage Moisture for Combination Sepa- 
rating and Throttling Calorimeter. Quality of steam Xi is 
calculated for a combination calorimeter as follows: 

Let Wi= weight of moisture collected in the separating 
calorimeter in a given time, in pounds. 
w 2 = weight of dry steam condensed after passing 

through the throttling calorimeter, in pounds. 
x 2 = quality of steam discharged from separating por- 
tion as determined by the throttling calorimeter, 
then without sensible error the percentage of 
moisture in the steam is, 

1-.,-- ?- + *, 

' Wl+W 2 

and in terms of "quality," we have also approximately, 

W 2 1 / n 

Xi = ■ hxs. 1 (4) 

Wi+w 2 

Still another type of combined calorimeter is illustrated in 
Fig. 59. In this instrument, known as Ellison's Combined 
Throttling and Separating Calorimeter, the sample of steam is 
collected by the perforated tube in the main steam pipe. The 
temperature before expansion in the throttling plug is indi- 
cated by the thermometer marked T 1; and another thermom- 
eter T 2 gives the temperature after throttling. A scale S 
opposite the glass water gage G is used to show the weight of 
water separated from the steam. The proportion of moisture 

1 If the radiation test shows it is large enough to be appreciable, then 
if R is weight of condensation due to radiation in pounds in a given 
time corresponding to that for the other units, then 

W 2+ R , . s 



DETERMINATION OF THE MOISTURE IN STEAM 



01 



separated in relation to 
the weight of steam passing 
through the instrument is 
the percentage of moisture 
separated. This percent- 
age is to be added to the 
percentage of moisture de- 
termined by throttling as 
calculated from the read- 
ings of the thermometers. 
Electric Steam Calorim- 
eters. For use with partic- 
ularly very wet steam, the 
Thomas electric calorim- 
eter, Fig. 60, has been 
designed. It consists es- 
sentially of a cylindrical 
vessel B containing a series 
of resistance coils for heat- 
ing steam by means of the 

iT 




Fig. 



Perforated Casing 
Filled with C 
Gauze. 




Fig. 60. — Thomas' Electrical Steam 
Calorimeter. 



59. — Ellison's Improved Steam 
Calorimeter. 

electric current passing 
through them.. These coils, 
are connected to the elec- 
tric terminals or binding- 
posts shown in the figure, 
and are supported in a 
soapstone cylinder in which 
there are a large number 
of £-inch holes through 
which the coils pass. 

Steam enters at the 
bottom of the vessel at 
A and passing upward 
through the heated coils 
the moisture contained in it 
is evaporated. The steam 
then passes- up through a 
perforated casing filled with 
copper gauze and escapes 
through the pipe discharg- 



62 POWER PLANT TESTING 

ing at the side at C. A part of this latter pipe is made 
of a glass tube for observing the condition of the steam. A 
thermometer is inserted at T for observing the temperature 
of the steam after this reheating. 

Although this apparatus is used for steam of high qual- 
ity as well as low, it has not been generally used to any 
great extent, probably because throttling calorimeters are 
preferred because of the greater simplicity and because very 
often a source of electric current is not conveniently available 
where tests are to be made. No data are available comparing 
its efficiency with that cf the combined separating and throttling 
calorimeters described in the preceding paragraphs, but for 
accurate tests the latter are generally preferred by engineers. 

Barrel Calorimeters. There is still another kind of steam 
calorimeter, known as the barrel type, deserving some attention. 
It is one of the oldest forms of apparatus for making deter- 
minations of the quality of steam. In the classification made 
at the beginning of this chapter it belongs in the group of con- 
densing calorimeters. Even with expert manipulations, ordi- 
narily it is much less accurate than any of the calorimeters 
already described. A typical apparatus of this kind is shown 
in Fig. 6 1. It consists usually of a weighing barrel B, made 
of three concentric vessels of galvanized iron with the two 
annular spaces between the inner and outer vessels filled with 
pressed sheet cork or hair felt to reduce radiation to a mini- 
mum. It is usually arranged so that when the inner vessel has 
been nearly filled with water from the barrel A, a quantity of 
the steam to be tested can be passed into it. The steam is 
admitted into the barrel in the most common forms by dis- 
connecting the water hose R at C and making a temporary 
connection from the steam pipe out of which a sample is to be 
taken to a vertical pipe in the barrel of sufficient length to 
extend nearly to the bottom of the inner vessel. The pipe may 
be plugged at the lower end and sufficient area for the escape 
of steam is then secured by drilling into the pipe a number 
of £-inch holes for some distance from the lower end. This 
arrangement will make it easier to secure an equal rise in 
temperature in the different parts of the barrel. A float is 
usually provided to show the depth of water in the barrel, and 
a suitable stirring device or agitator consisting of paddles 



DETERMINATION OF THE MOISTURE IN STEAM 



03 



attached to a vertical shaft is also needed. This agitator when 
revolved stirs up the water and brings it to a constant 
temperature. 

Briefly the method to be pursued in the operation of the 
barrel calorimeter may be outlined as follows: First fill the 
barrel with cold water till the float shows that the water level 
is within about 6 inches from the top. Then stir well, observe 




Fig. 6i. — Barrel Steam Calorimeter. 



the temperature accurately and weigh carefully on a platform 
scales. The steam pipe should then be connected up to dis- 
charge into the water after first allowing the steam to blow off 
into the air, for the purpose not only of removing the condensa- 
tion in the piping, but also to heat it to as nearly as possible 
the temperature of the steam. When the temperature has risen 
to about 1 20 degrees Fahrenheit the steam should be shut off 
and another weighing made to determine the amount of steam 
added. While the weighing is being done the water should be 



64 POWER PLANT TESTING 

stirred vigorously and the highest temperature observed. For 
all the weighings the piping must be in exactly the same position 
as regards the connection on the barrel and all the pressure 
in the pipes must be relieved. When the piping between the 
calorimeter and the steam supply is connected by pipe fitters' 
unions these should be disconnected to insure the best accuracy. 
When, however, the connection is made by means of flexible 
rubber hose the weight can probably be obtained accurately 
enough without disconnecting the piping if the precaution is 
taken to relieve the pressure in the piping by opening a petcock 
located in the steam pipe near the point where it enters the 
barrel. 

If, just before making the test for the quality of the steam, 
the calorimeter is filled with water, heated with steam or other- 
wise to about 1 50 degrees Fahrenheit and again carefully drained, 
the barrel will be near its average temperature during the test, 
and no correction need probably be made for the heat absorbed 
by the calorimeter. In most cases it is preferable, however, to 
determine accurately the heat absorbed by the calorimeter and 
then make the proper corrections ; but unless the work be done 
very carefully it is valueless. This correction is usually made 
by calculating the water equivalent or the capacity of the 
calorimeter to absorb heat measured by the similar capacity 
of water. This water equivalent is to be added to the weight 
of water in the calorimeter. Using then the following symbols: 

w' = weight of water in calorimeter in lbs. 
w" = weight of water added in lbs. 

t' — temperature of water in calorimeter, deg. Fahr. 
t" — temperature of water added, deg, Fahr. 
t'" = temperature of mixture, deg. Fahr. 

k = water equivalent in lbs. Then 

(w'+k)(t'"-t')=w"(t"-t'"), 

, w"(t"-t''") 

k= t /„_ t / — -W, • ...» (5) 

The temperature of the water added should be taken just 
as it enters the calorimeter and as near to it as possible. 

The quality of the steam (x ) to be determined is calculated 
as follows : 



DETERMINATION OF THE MOISTURE IN STEAM 65 

Wi = weight of water in calorimeter in lbs. 
W2 = weight of steam added, in lbs. 

k = water equivalent of calorimeter in lbs. 

t x = initial temperature of water in calorimeter, degs. Fahr. 

t2= final temperature of water, degs. Fah. 

Po== pressure of steam, lbs. per sq.in. 

ro = heat of vaporization of steam (B.T.U.) corresponding to 

Po- 
qo and q 2 =^ sensible heat of steam (B.T.U.) corresponding 
to po and t 2 . 

Then equating the heat lost by the steam to the heat gained 
by the water 1 , 

(x ro+qo-q2)w 2 =(wi+k)(t2-ti). ... (6) 

(w 1 +k)(t a -t 1 ) + qg-go ( ) 

w 2 r r 

The accuracy of this instrument depends principally on the 
accuracy with which the various temperatures and the weight 
of the condensed steam are obtained. Usually it is very dif- 
ficult to obtain accurately the temperature of the mixtures of 
water and steam. It is not unusual for determinations of 
moisture with such a calorimeter to vary for the same quality 
of steam and with expert handling as much as 5 per cent. In 
the case, therefore, of steam with 10 per cent moisture, the deter- 
mination of quality might be in error as much as one-half per 
cent. 

Calorimeter Calibrations. For a laboratory calibration 
exercise three calorimeters of different types are connected 
by means of exactly the same kind of fittings and valves 
to the same steam main or receiver. A water-jacket or a 
device like that shown in Fig. 34 should be provided to vary 
the quality of the steam. Tests should be made simultaneously 
and for the same length of time on the three instruments. 

1 Equation (7) can be made a little simpler for calculations by writing 
for (q 2 — q ) the difference between the corresponding temperatures 
Ct 2 — 1 ) without appreciable error. 



CHAPTER IV 
MEASUREMENT OF AREAS 

Planimeters. The most accurate and generally approved 
method for obtaining the area of irregular figures is by means 
of integrating instruments called planimeters. Instruments 
of this kind may differ in many details, yet all of them are based, 
in theory, on the original Amsler polar planimeter. 

Polar Planimeters. One of the simplest forms of the polar 
type of planimeters is shown in Fig. 62. It consists essentially 




Fig. 62. — Amsler Polar Planimeter. 

of two arms PO and TO pivoted together at 0. When in use 
the point P is not to be moved, and is held in place by means of 
a pin-point upon which a small weight rests. There is a tracing 
point at T intended to be moved around the border of the area 
to be measured. Attached to the arm TO is a small graduated 
wheel W carried on a short axis which must be placed accurately 
parallel to TO. Any movement of the arm TO except in the 
direction of its axis will, of course, move the wheel W on the 
paper or other surface on which it is placed so that the amount 
of its movement gives a record indicating the area measured. 
A vernier, V, placed opposite the graduations on the wheel, 
assists in reading the instrument accurately. The arm TO 
is usually made of such a length that the movement of the trac- 
ing point T around an area of one square inch (for English 

66 



MEASUREMENT OF AREAS 



67 



units) will move the wheel one-tenth of its circumference. 
Graduations of the vernier indicate usually one one-thousandth 
of a revolution of the wheel, or in English units one one- 
hundredth of a square inch. 

When the tracing point T is moved around an area in a 
clockwise direction the wheel will roll in the direction of its 
graduation, and the area is found by subtracting the final reading 
from the initial. Amsler planimeters are often constructed with 
the arm OT adjustable in length, so that it can be set to indicate 
areas in various units, as, for example, square inches, square 
feet, square centimeters, etc. 

The veriner V has ten graduations, and the total length 
of these ten divisions is one-tenth less than the length of those 
on the wheel, so that it repre- 
sents, counted from zero, so 
many hundredths of an inch. 
To explain the method of using 
the vernier, Fig. 63 has been 
inserted, showing the wheel W 
and the vernier V, in a drawing 
of larger scale than in Fig. 62. 
Readings of the graduations 
on the wheel W are always 
taken opposite the zero mark 
on the vernier, so that the 
reading indicated in Fig. 63 
without the help of the vernier 

would be little more than 4.7. The graduation on the vernier 
which is exactly coincident with a graduation on th e roller wheel 
is the third from zero and indicates three hundredths. The 
complete reading is therefore 4.73 as determined by the vernier. 

Theory of Polar Planimeters. As this instrument is con- 
structed neither of the points T nor W can pass over the arm 
PO (Fig. 64). If the arms PO and TO are clamped so that 
the plane of the graduated wheel W intersects the point P ; 
that is, when the angle TWP is a right angle, and then the 
arms thus clamped are revolved around this point, the wheel 
will be continually slipping without any rolling motion in the 
direction of its axis, and consequently it will not revolve. 
When, however, the arms are not clamped and if the con- 



-J xc- 



I 



Fig. 63. 



-Typical Vernier for 
Planimeter. 



POWER PLANT TESTING 




a, 

P w 

Fig. 64. — Position of the Arms of 
a Polar Planimeter to Draw the 
"Zero" Circle. 



struction of the instrument will permit the tracing point 

T to be moved out so far 
~~~~---^ that the axis of W will lie 

in the line PO, then an arc 
\ described by the movement 

of T will produce only a 
rolling motion of the wheel. 
Obviously with the arms in 
any position intermediate be- 
tween that of the clamped 
right angle and the one with 
W in line with PO, the wheel 
will partly slip and partly 
roll, the amount of slipping 
and rolling depending on the 
size of the angle between the 
arms. It follows, then, that 
when circumscribing a closed 
figure, the radial components 
cause only slipping of the 

wheel and need not be considered, while the circumferential 

components produce a result- 
ant rolling which must be 

taken into consideration. 
The path described by the 

tracing point T when the 

arms are clamped as indicated 

in Fig. 64, is called the zero 

circle for the planimeter. If 

the tracing point is moved 

in any path outside the zero 

circle in a clockwise direction 

a positive record will be indi- 
cated on the graduated 

wheel, while if it is moved 

in a path in the same direc- 
tion as before but inside the 

zero circle, there will be a 

negative record. 

According to the theory of polar planimeters, they are 




Fig. 65. — Theoretical Diagram for 
a Polar Planimeter. 



MEASUREMENT OF AREAS 69 

designed so that the rolling of the wheel for a given circumferen- 
tial motion of the tracing point T is proportional to the area 
included between the path of T, the radial line from P (Fig. 65) 
to the initial and final points of the path taken by T, and the 
arc of the zero circle included between these radial lines. In 
the discussion of this theory, circumferential motion of the 
tracing point T around the point P, and the angle WOP 
(marked a) remaining always at a constant value, is to be taken 
up first. 1 Now let us suppose the tracing-point is moved from 
T to T' in the figure through a very small angle, TPT' (marked 
e), keeping, however, the angle a constant, then the graduated 
wheel W will move through the arc WW, partly rolling and 
partly slipping. The component of this motion producing 
rolling will be perpendicular to the axis of the wheel; or, in 
other words, this component will be perpendicular to OT in 
all its positions, and without appreciable error for small values 
it may be represented in this figure by the line WX, making 
WXW' a right-angled triangle of infinitesimal proportions. 
When the tracing point has moved from T to T' the point 
has moved through the arc 00' and the tracing, point subtends 
in its movement an angle WPW, which is equal to the angle 
TPT', marked e, which was passed over by T. Then the follow- 
ing relation is easily obtained: 

WW' = PW'Xc. 

The symbol c is constant, expressing the ratio for a given angle 
WPW between the length of an arc and the corresponding radius for 
any value of this radius. In other words in terms of the calculus this 
constant would be expressed in radians. In general for every angle 
there is a constant value which when multiplied by the radius gives the 
length of the arc for that radius. 

The component of WW' corresponding to the rolling of the 
wheel is WX, which is approximately equal to the arc WW 
times cos WWX. That is, 

WX = PW'XcXcos WWX . . . . (0) 

But if PY is drawn perpendicular to T'W produced 

PW'cos WWX = WY, (9) 

1 In the mathematical discussion following, the graduated wheel 
will be considered as if it were a part of the arm TO, with its plane 
exactly at right angles to the axis of this arm. 



70 POWER PLANT TESTING 

and combining (8) and (9) , 

W'Y = ^ . . . (10) 

c 

Since the angle WPW is very small, WW may be taken as 
being perpendicular to W'P. Now WX is perpendicular to 
T'Y and the angle W'WX is equal to the angle PW'Y. The 
trigonometric relations reducing the above to terms of the 
length of one of the arms of the planimeter and the constant 
angle a are as follows : 

WT = — = PW cos PWY = PO' cos PO'Y- WO' 
c 

= PO' cos a -WO', 

then WX = c(PO'cosa-WO') (11) 

This is an expression for the amount of rolling of the wheel 
when the tracing-point moves from T to T'. 

To express the relations required the area will now be 
expressed trigonometrically in similar units. From geometry 
the area of sector TPT' = i/2 arc TT'XPT, but arc TT' = 
PT X c (see page 69) , or area TPT' = 1/2 c XPT 2 . 

We can write also, 



PT = v' PO 2 + OT 3 + 2PO X OT cos a, 

area TPT' = i/2 c (PQ 2 +OT 2 + 2POXOT cos a). . (12) 

But the area represented by the amount of rolling of the 
graduated wheel is that part of the sector outside the zero 
circle (see page 71), and this is the area TT'Q'Q. Now the 
radius r of the zero-circle, referring again to Fig. 64*, is 
easily obtained from equations expressing the relations of the 
sides of the right triangles in that figure for the particular 
case when there can be no rolling movement. Thus, 

P0 2 = W0 2 + PW 2 , (13) 

PW 2 = PT 2 -WT 2 = PT 2 -W0 2 -2W0X0T-0T 2 . . (14) 

* It will be remembered that with the arms of the planimeter in the 
position shown in Fig. 64 the tracing point T describes the circumference 
of the zero circle. 



MEASUREMENT OF AREAS 71 

Combining equations (13) and (14), 

PO 2 = WO 2 + PT 2 - WO 2 - 2WO XOT - Of 2 . 

But PT = r, the radius of zero-circle, therefore, 



r = \ P0 2 + 2W0X0T+0T^ (15) 

Also from geometry, as explained on the preceding page, 
Area QPQ' = i/2 rXcXr = i/2 cXr 2 

= 1/2 c(P0 2 + 2WOXOT+OT 2 ). (16) 

Subtracting equation (16) from equation (12). 

AreaQTT'Q , = cXOT(POcosa-WO). . . (17) 

Equation (17), which is the expression for the area outside the 
zero-circle, will be observed to be equivalent to the roll of the 
graduated wheel as given in equation (11), times the length of 
the arm OT from the pivot to the tracing-point. If, therefore, 
for a given area A, we call the reading of the wheel R and the 
length of the arm from pivot to tracing-point L, then, 

A = LR (18) 

It should be noted further that this equation is independent 
of any other dimensions of the instrument. 

That this demonstration applies to areas not adjacent to 
the zero-circle or partly inside and out can be readily shown 
by subtracting in a given case the area between the zero-circle 
and the required area. 

Area of Zero Circle by Experiment. The area of the zero- 
circle of a planimeter may be found readily by passing the 
tracing-point around the circumference of two circles each 
larger than the zero-circle. Preferably for this operation the 
fixed point of the instrument is placed at the center of the 
circles. If the calculated areas of these circles are respectively 
Ax and A 2 , and r is the radius of the zero-circle, then since 
readings of the graduated wheel show only the areas outside 
the zero-circle represented by R^ and R 2 , we obtain, 

Ai=7rr 2 +Ri, 

A 2 = 7rr 2 +R 2 , 
277r 2 = A 1 +A 2 -(R 1 +R 2 ). . . . . . . (19) 



72 POWER PLANT TESTING 

After r has been found 1 it is not difficult to calculate the proper 
length of thearm OT for any linear units (compare equation 15). 
In fact very many polar planimeters are constructed with an 
adjustable arm OT, so that the instrument can be used for any 
scale or for various units. The exact lengths required for both 
the English and metric units (inches and centimeters) are 
usually stamped on the adjustable arm. 

Mean Ordinate of an Area. 2 If we call m the mean ordinate 
and 1 the length of a given area A, then 

A = ml. 

From equation (18) we have, 

A = LR, 

whence 

ml = LR, 

m = -R (20) 

When, therefore, the tracing-point arm is adjustable it may be 
set as shown in Fig. 66 3 to make it equal to the length of 

1 If instead of measuring and calculating the circles both larger than 
the zero-circle, one of the two is made smaller than the zero-circle, then 
the reading of the instrument is again the difference between the area 
of the circle and that of the zero-circle, but the value of this difference 
is now negative, so that if A t is the area of the circle larger than the 
zero-circle and A 2 is the area of the one smaller, then using the other 
symbols as before, 

A 1 =7rr 2 + R 1 , 
A 2 = 7rr 2 -R,, 

27tr 2 = A t + A, - (R x -R 2 ) . 

Although this latter method does not fall in with the general demon- 
stration so Avell, it is, however, usually preferred, as it will give greater 
accuracy than can be obtained with two circles both larger than the 
zero-circle, unless one of these is made unusually large. 

2 Engineers must calculate mean ordinates most often when deter- 
mining the mean effective pressure (M.E.P.) of engine indicator dia- 
grams. 

3 To facilitate the adjustment of the arm to the length of the diagram 
or area measured, sharp points M and N are attached to the back of 
some planimeters. The point M is often conveniently placed a short 
distance away from the tracing-point T, and the point N must then be 
the same distance and in the same direction away from the pivot 0. 
Then obviously the distance between M and N will be in all cases equal 
to the length of the adjustable arm. 



MEASUREMENT OF AREAS 



73 



the area measured. Then, obviously, the height of the mean 
ordinate will be equal to the reading of the graduated wheel 
expressed in the same units. For example, if the subdivi- 
sions of the wheel are fortieths of an inch, the result will be 
the mean ordinate also in fortieths. This scale of the wheel 
is not determined by the diameter of the portion of the wheel 
which is graduated, but by the diameter of the edge which 
comes into contact with the surface over which the wheel rolls. 
If then d is the so-called diameter of "rolling" of the wheel, 
its circumference is 7rd. Now by dividing the number of divi- 
sions on the circumference (usually ioo) by nd, the " scale " 




Fig. 66. — Polar Planimeter with Adjustable Arms for the Rapid Deter- 
mination of Mean Ordinates. 



of the wheel is obtained. It may also be found by measuring 
a rectangular area of the same length as that of the tracer arm 
and one inch wide, when the reading from the wheel will give 
the number of divisions per inch. For those instruments of 
which the radius of the wheel is one centimeter (.795 inch diam- 
eter) and having 100 divisions, the scale is almost exactly 40 
divisions to the inch. 

Coffin Planimeter and Averaging Instrument. This planim- 
eter is made commonly in two forms, illustrated by Figs. 67 
and 68. As regards details the former is somewhat the simpler 
and will be explained first. In principle the two are exactly 
alike. As will be observed in the figures, this instrument has 
a single arm to which a suitably graduated wheel is attached 



74 



POWER PLANT TESTING 



on an axis parallel to the line joining the ends of the arm. One 
of the ends of this arm is for tracing the outline of the area 
measured while the other slides up and down in a suitable slot. 
One of the advantages of this instrument over the polar planim- 
eter, although it is not so generally adaptable, is that the 
wheel is made to move over a specially prepared surface, pre- 
venting unnecessary slipping. On materials having a rough, 
fibrous, or worst of all, an uneven surface, the movement of 
the wheel of any planimeter will not be the same as when rolling 
over a smooth fiat surface. 



; i;r. : -i^ 



J 







Fig. 67. — Coffin Planimeter. 



Fig. 68.— Coffin-Ashcroft 
Averaging Planimeter. 



The Coffin planimeter may be discussed as a special form 
of the general polar type in which the pivoting point 0, instead 
of swinging about the fixed point P (Fig. 62) moves back and 
forth in a straight line. The angle between the arms PO and 
OT, as indicated by the dotted lines in Fig. 69, is really invari- 
able at 90 degrees. Obviously, then, the equation (17) express- 
ing the area traced by a polar planimeter outside the zero 
circle becomes, referring to Fig. 65, 

area = cX0T(-W0), 

likewise equation (11), expressing the roll of the wheel for the 
Coffin planimeter, becomes equivalent to, 

Roll or record of the wheel =c(-W'0')=c(-W0). 



MEASUREMENT OF AREAS 75 

Using, as before, in equation (18), the symbols L and R for, 
respectively, the length of the arm OT and the reading of the 
wheel, we have, just as for the polar planimeter, 

A = LR (21) 

As an averaging instrument the Coffin planimeter is very much 
more convenient than the typical forms of polar planimeters. For 
finding the mean ordinate of an area the use of the polar type of 
these instruments was explained on page 72. The sliding 
vertical straight edge shown at the right in Figs. 67 and 68 is 



p \ 




Fig. 69. — Theoretical Diagram for a Coffin Planimeter. 

for the purpose of making the operation of finding the mean 
ordinate of an area (or the " mean effective pressure " of an 
engine indicator diagram) as simple as possible. For this 
operation the straight edges C and K should be adjusted so 
that when the tracing pin passes over the extreme end of the 
area to be measured it will just touch both of them. Now if 
the tracer is started at either end of the area and moved around 
to the starting point and then moved upward along the vertical 
straight edge until the reading of the wheel is the same as when 
starting to trace the area, this last distance traced from the 
starting point along the vertical straight edge is the mean ordi- 
nate. To demonstrate this statement the symbols used on page 
72 will be continued. Representing the mean ordinate by m, 
the length of the area A by 1, the reading or rolling of the gradu- 



76 



POWER PLANT TESTING 



ated wheel in going around the area by R, and the length of 
the arm carrying the tracer by L, then as before 

A = ml. 

Now, when the tracing-point T moves over a vertical 

line, the angle DOT, repre- 
sented by Z in Fig. 70, re- 
mains constant. If we call 
the vertical distance moved 
v, and remember that only 
the movement of the wheel 
at right angles to its axis 
produces rolling, then the 
reading corresponding to the 
rolling, R, is, 




R = v sin z. 



(22) 



But for the position shown 
in Fig. 69 when the tracer 



Fig. 70.— Theoretical Diagram for T is at the right-hand end 



Coi'fin Planimeter. 



of the outline of the area, we 
have 



whence 



sin z = T , 



vl 



Substituting this value of R in the general equation (20) for 
the mean ordinate m of a polar planimeter, then, 



L vl 
m= yir v. 



(23) 



This relation can be illustrated more simply, however, by 
referring to Fig. 71, which is typical indicator diagram from 
a steam engine. In this figure the tracing point of the Coffin 
instrument is shown at 0, with the tracing arm represented 
by VO. A rectangle OXYZ, indicated by dotted lines, is shown 
of which the area is equal to that of the indicator diagram. 



MEASUREMENT OF AREAS 



77 



Starting at and moving the tracing point around the indicator 
diagram once the difference in readings is the area. Now if 
the tracing point is moved in the opposite direction around 
the rectangle and again back to the starting point at it will 
measure a negative area equal to the first area and the reading 
of the graduated wheel will be the same as when first started 
around the indicator diagram. The movement of the graduated 
wheel as the tracing point moves from X to Y is equal and 
opposite to that in going from 
Z to 0, so that these two cancel 
each other. The motion of the 
tracing point from Y to Z re- 
quires the axis of the graduated 
wheel to be parallel to YV and 
consequently during this move- 
ment the wheel will not be 
moved. The only movement 
that is therefore producing a 
net change in reading of gradu- 
ated wheel during the reverse 
tracing of the rectangle is in 
going from to X. Conse- 
quently after going around any 
irregular area like an indicator 
diagram in a clockwise direction 
from the starting point at 
at the right-hand end of dia- 
gram, if the tracing point is 
moved in a vertical direction 
from the starting point at 

until the reading of the graduated wheel is the same as when 
first started, this vertical distance moved, measured from 0, 
will be equal to the mean height of the indicator diagram. 

Although measurements of areas may be made with the 
Coffin planimeter as with the regular polar types with the area 
in any position as regards its length and breadth, yet when the 
mean ordinate is to be obtained, its value in a definite position 
is required and the area must be placed so that its length with 
respect to which the mean ordinate is to be obtained will lie 
along the horizontal straight edge shown in the figures. Then 




Fig. 7 1 . — Diagram Explaining the 
Method of Mean Ordinates with 
a Coffin Planimeter. 



78 



POWER PLANT TESTING 



the mean ordinate measured along a vertical straight edge will 
give the result required. 

Roller Planimeters. For the measuring of very large areas 
a planimeter differing slightly in theory from the polar type 
has been designed by G. Coradi, of Zurich, Switzerland. It 
has the advantage of being adaptable for measuring surfaces 
of indefinite length and as wide as the length of the tracer arm. 
This instrument is illustrated in Fig. 72. This instrument is 
supported at three points — the two rollers R 1 and R 2 and the 
tracing pin f, or its support s. These two rollers are attached 









/@}/p=== 


1 (f 1 — 1 1 L 


1 9 


© _ 




III p' 


QCz^ 1= 


t 


V 


f B il R 




1 lU^=- 


' j ,iP '||4b 



Fig. 72. — A Typical Roller Planimeter. 



to the shaft A. On the face of one of these rollers is a 
minutely divided miter-wheel engaging with a small pinion 
revolving the horizontal shaft carrying the spherical segment 
K. At the center of the frame B, and in the same vertical 
plane with the two shafts already mentioned, a vertical shaft 
carrying the tracer arm is supported. The spherical segment 
K causes merely by friction contact the movement of the 
cylindrical " measuring " roller shown at its right. This 
roller is supported on the auxiliary frame M, of which the 
tracer arm is a part. The " measuring " roller moves back and 
forth with respect to the spherical segment to correspond 
with the movement of the tracing point ; but at the same time 



MEASUREMENT OF AREAS 



79 



■I 1 1 



Fig. 



-Planimeter Testing Rule. 



the rotation of the segment itself imparts rolling motion of 
the entire instrument. 1 

Testing Planimeters. Tests are made by comparing the 
readings of the instrument with that calculated for a given 
area. For such cali- 
brations it is neces- 
sary to use an area 
which can "be gone 
over accurately with 
the tracing point pref- 
erably held mechanically. This is done usually by using a 
metallic testing rule shown in Fig. 73. It is usually made in the 
shape of a narrow strip from three to five inches long. At the 
end marked zero on the graduations a needle point is set which 
is kept in place by an overlapping screw. At each line of 
the graduations there is a very small conical hole into which 

the tracing point of the pla- 
nimeter can be placed. The 
beveled end of the testing rule 
has the index line to be set 
accurately at the starting 
mark, so that this point can 
be very carefully located. 
"With the tracing-point T in 
the testing rule and the fixed 
point P of the planimeter in 
approximately the position 
shown in Fig. 74, observe the 
reading of the instrument 
corresponding to the area of the circle described by the tracer 
moving clockwise, in the positions shown. 

1 st. When the fixed point P is on the left-hand side of the 
tracing point. 

2d. When P is on the right-hand side. 

If the reading obtained is greater in the first position than 
in the second, the end of the shaft carrying the graduated wheel 




Fig. 74. — Methods of Testing 
Planimeters. 



1 Since this instrument is not often used by engineers, those interested 
in its theory are referred to Coradi's book of directions (in English) 
accompanying each instrument, or to Handbuch der Vermes sungskunde, 
byW. Caville. 



80 POWER PLANT TESTING 

nearest the tracing point must be shifted toward the right to 
make the instrument accurate, and vice versa. Otherwise the 
error, if there be one, can be eliminated by taking the mean 
of the results obtained for the two positions 1 . 

Another test to be made, if there is doubt about the accuracy 
of a planimeter after the axis of the wheel has been adjusted, 
is to determine whether the settings of the adjustable arm 
marked on the instrument are correct. For this determination 
circles with several different diameters can be measured with, 
the testing rule, and if there is a nearly constant percentage 
error, say x per cent too large, then the adjustable arm must 
be lengthened x per cent to make the planimeter readings 
correct, and vice versa. 

For accurate results the fixed point P should be placed as 
indicated by the dotted lines in Fig. 74, so that when the tracing 
point is near the center of the area to be measured the two arms 
will be approximately at right angles. 

Durand-Bristol Integrating Instrument. This instrument, 
illustrated in Fig. 75, has been recently developed by the Bristol 
Company for obtaining the average radius of records traced on 
circular charts of uniform graduations like those used in re- 
cording gages and thermometers, etc. It is a simple device 
for obtaining quickly the average value of pressure, temperature, 
draft, watts, volts, amperes and other records generally taken 
on circular charts. 

This instrument consists of a wooden base in which there is a 
metal socket for supporting a rotatable pin slotted for receiving a 
horizontal shaft to which the integrating wheel is rigidly attached. 
On this shaft between the integrating wheel and the pin there 
is an adjustable tracing point and at the opposite end of the 
shaft there is a triangular support for the shaft, also adjustable. 

The general principle of this instrument is due to Professor 
W. F. Durand 2 of Leland Stanford University. Its application 

1 For ordinary requirements a testing disk can be used in place 
of the rule, although it is not usually so accurate. On this disk circles 
of 1, 2, and 2 J inches diameter are usually engraved; and if neither a 
testing plate nor a disk is available, rough tests can be made by using 
circles drawn with a pencil compass on a flat sheet of well-calendered 
paper. 

2 Proceedings American Society qf Mechanical Engineers, October, 
1908, pages 1241-1246. 



MEASUREMENT OF AREAS 81 

hinges on the condition that the chart to be measured has a 
uniform radial scale, the same as there must be a uniform 
vertical scale for indicator and other similar diagrams in order 
that they can be averaged with the ordinary planimeters. Ob- 
viously the mean value of the radius of a circular diagram can- 
not be determined with ordinary planimeters, since the area of 
a diagram in polar co-ordinates is proportional to the square 




Fig. 75. — Bristol-Durand Integrating Instrument for Circular Charts. 

of the radius and to the angle. 1 In Fig. 76, AB is an irregular 
curve, considered for this theoretical discussion as traced by a 
point moving in and out on a straight radial line. The center 
of the chart is at 0, and at this point there is a socket, in 
which a rod O'P slides freely back and forth, permitting a tracing 
point, P, to draw a curve AB. A graduated wheel, W, attached 
to O'P, serves the same general purpose as the integrating wheel 
in the ordinary planimeter. Obviously this wheel will be moved 
only by circumferential motion, and for any radial movement 
of the rod in the direction of its length it will remain stationary. 

1 With the ordinary planimeter the mean square of the radial ordi- 
nates can-be determined, and we can, of course, take the square root of 
these values, but in most cases this is not the same as the mean radius. 



82 



POWER PLANT TESTING 



The amount of movement will be proportional to the radius 
WO, which differs from PO by a constant distance PW. Result- 
ant movement of the wheel W is proportional, therefore, to 
the angle moved through by the arm O'P and to the radius OW 
varying from point to point along the curve. Assuming for 
the present, but as will be shown later the reading for any pare 
of the curve, as AB, to be proportional to the product of tht 
angle subtended between the points A and B, AOB, and the 
mean radius for the curve between these points, then if 
this reading is divided by the subtended angle expressed 




Fig. 76. — Diagrammatic Drawing of Bristol-Durand Integrating 

Instrument. 

in circular measure the quotient will be proportional to the 
mean radius. Now if to the value of this mean radius the 
constant distance WP is added, the true value of the radial 
ordinate OP is obtained. When, as is usually the case in prac- 
tice, the curve AB, represents values of radial ordinates with 
reference to a base circle of constant radius as the datum or 
" zero line," then if the radius of this base circle is subtracted 
from OP the remainder will be the true value of the ordi- 
nate. By making WP equal to the radius of the base circle, 
as may readily be done by a suitable adjustment of the instru- 
ment, the two corrections will be "balanced " and the mean 
value of the radial ordinate will be given directly as the quo- 
tient of the reading of the wheel and the subtended angle AOB 
expressed in circular measure. For a chart corresponding to 



MEASUREMENT OF AREAS 



83 



twenty-four hours for a circumference, the angular measure 
to be used as the divisor will be .2618 per hour. 

The quantity to be determined in such diagrams is the time 
mean of the quantity measured by the radial ordinate. But since 
angular motion is made proportional to time, we may represent 
the desired mean by the following integral formula : 



fa 



(24) 



Now, in Fig. 77, let ABCD denote a curve drawn by a tracing 
point which moves on the arc of a curve shown by OAV instead 
of on a straight radial line. 
Then let OV, ON, OM, etc., 
denote a series of consecutive 
positions of the curve OAV, 
at differential angular inter- 
vals dd. Then for the actual 
curved path ABCD substitute 
the broken line path made up 
of a series of arcs each rd# in 
length, and the series of differ- 
ential bits of the curve OAV as 
shown. Then at the limit the 
record of any integrating or 
averaging instrument will be 
the same, whether the tracing 

point is carried along the curve or along the broken line substi- 
tute as shown. 

Then suppose an integrating instrument, as shown in Figs. 
75 and 76, is applied to such a diagram, and let the tracing point 
P be carried along the zig-zag path. The record of the wheel 
will be made up of two parts : 

1. That due to the circular arcs rd# and representing by 

summation the value of ( rdO. 




Fig. 77. — Theoretical Curves for 
Bristol-Durand Instrument. 



/' 



2. That due to the differential portions of the arc OAV. 
Now it is clear that if the diagram extends all the way around 
from A through BCD to A again the differential elements of the 



84 POWER PLANT TESTING 

curve OAV may be considered as existing in pairs, and that for 
every element traversed in the outward direction, there will 
be an equal element traversed in the inward direction. PQ and 
ST denote the members of such a pair. The record for such 
a pair will therefore disappear in the summation, and hence 
for all the pairs, and hence for the diagram as a whole. In such 
a case, therefore, part " 2 " above becomes zero and the record 

of the wheel for the entire diagram consists simply of J rd#. 

This reasoning is seen to be entirely general and independent of 
the character of the path OAV, and hence must be true whether 
it be the arc of a circle, a straight line or any other path. 

In case the curve occupies only part of the revolution, as 
ABC, then it is clear that in going from A to C the record 
will involve the two parts, " 1 " and " 2 " above, and that 
the latter will remain included in the final result and will 
represent the summation of the record due to the elements of 
OAV between A and C. This obviously will be the value of 



/ 



rdf) for the arc GC and it will be canceled by carrying the 



tracing point of the instrument back from C to G. This method 
of reasoning is independent of the extent of the arc and is there- 
fore equally true for an entire revolution, even when the diagram 
does not end at the same radial distance, as at the beginning. In 

such cases it is necessary only to trace along the arc OAV so 
as to " close " the curve, thus canceling part " 2 " above and 



finding directly the value of I rdO for 



a whole revolution. 



In all cases the correction for part " 2 " of the record is 
made by tracing from the terminal point of the curve along the 
path, representing no change of time to a point lying in a circum- 
ference passing through the initial point. This may be stated 
in other words by saying that to eliminate part " 2 " of the 
record the tracing point must start and finish at the same 
distance from the center, and if the diagram is not of the kind 
to satisfy this condition then the necessary portion of a path 
of zero change of time must be used to supplement the diagram. 
This discussion is independent also of the nature of the curve 
OAV. It may be stated, however, that when OAV becomes a 
straight line the value of the correction becomes zero. 



CHAPTER V 
ENGINE INDICATORS AND REDUCING MOTIONS 

The engine indicator is simply an instrument showing by 
graphic diagrams the variations of the pressure in the engine 
cylinder of steam, gas, air, or whatever the working substance 
may be. Before James Watt invented the engine indicator 
(about 1 814) he had already used a steam pressure gage on the 
cylinder of his engine, and since the movement of the piston 
in the early steam engines was very slow, he was able to observe 
with his eyes how the pressure varied during a stroke of the 
piston. In modern engines the movement of the piston is so 
rapid, however, that a recording instrument is absolutely 
necessary. 

Watt's indicator is illustrated in Figs. 78 and 79. It con- 
sists of a cylinder CC (Fig. 79) in which the piston P is 
moved against the resistance of the spring S by steam 
pressure from the engine cylinder; this pressure being exerted, 
of course, on the lower side of the piston. A pencil attached 
to the : upper end of the piston rod traces on a sheet of 
paper a diagram DD, of which the height on any ordi- 
nate is' proportional to the pressure. The paper is moved 
back and forth on a slide by a string E moved in conformity 
with the piston. The instrument was of great service to Watt 
in perfecting his steam engines. In the modern indicators, of 
which a few of the best known makes are to be described, there 
are many improvements over the instrument used by Watt. 

Thompson Indicator. Of the engine indicators now in 
general use the Thompson is the oldest and best known. Fig. 
80 shows one view of this instrument and Fig. 81 shows the 
corresponding sectional drawing. 

It consists in essential parts of a piston, 8 (Fig. 81) moving 
in a cylinder 4. This piston is rigidly connected to the rod 
12, which passes up through the cap 2. The motion of the 

85 



86 POWER PLANT TESTING 

piston rod 12 is transferred to the pencil 23 by means of 
suitable links designed to make the pencil move parallel to but 
usually four times as far as the piston 8. The maximum pres- 
sure of the pencil on the paper used for the diagram is 
adjusted by the thread and set screw on the handle attached 
to the bracket X. 




Fig. 78. — Watt's Original Steam Engine 
Indicator (Type of 1814). 



Fig. 79. — Section of 
Watt's Indicator. 



The method of changing the springs in the various common 
forms of engine indicators should be well understood by everyone 
likely to be called on to " indicate " engines. When the work 
of changing springs is done clumsily or carelessly, a great deal 
of time is often wasted by the whole party engaged in the test. 
The method to be followed in changing springs of a Thompson 
indicator may be stated briefly as follows: The milled-edged 



ENGINE INDICATORS AND REDUCING MOTIONS 



87 



cap 2 should first be unscrewed from the top of the cylinder 
containing the spring and piston. This cap, together with the 
piston rod, piston, and link can then be lifted from the main 
body of the indicator. By unscrewing the small milled-headed 
screw 19, connecting the piston rod with the pencil arm the 
spring can then be unscrewed, first from the cap 2 and finally 
from the piston 8. By exactly reversing the operation another 




Fig. 80. — Thompson Indicator. 



spring can be put in the place of the one removed. Changing 
springs in this instrument is a simple operation. No wrenches 
or other tools are required. Care should be taken, of course, 
to screw up the spring firmly against both the cap and the piston. 
Probably one-half the troubles with indicators in operation 
arise from loose springs, although not so often probably, with 
Thompson indicators as with some other types. 

In selecting a spring for an indicator test it should be of 
such a scale that the largest diagram to be taken will not be 
more thai! if inches high ; that is, if the maximum pressure will 



88 



POWER PLANT TESTING 



be about 140 pounds, a spring with a scale of 80 pounds per 
square inch should be selected. The tension of the spring inside 
the drum carrying the paper for the diagram is varied by loosen- 
ing the thumb nut and turning the large milled cap till the proper 
adjustment is secured. 1 

Crosby Indicators. For high-speed engines and for accurate 
results the Crosby indicator has long been a favorite with 

engineers. This indi- 
cator is illustrated in 
Figs. 82 and 83. It 
consists of a piston 
8, moving in the 
cylinder 4, and is 
connected by means 
of the piston rod 10 
and the link 14 to 
the pencil lever 16. 
All of the pencil 
mechanism arranged 
to move the pencil 
point 23 in a straight 
line parallel to the 
motion of the piston 
8, is supported by 
the links 13 and 15 
on the sleeve 3. The 
indicator spring is 
fastened at its lower 
end to the piston by a 
ball-joint and at its upper end it is screwed into the cap 2. The 
method of attachment of the springs to the piston by means 
of the ball-joint is shown more in detail; in Fig. 84. 

In this indicator the spring is changed by first unscrewing 
the milled cap 2, then this cap, the sleeve 3, the piston rod 10, 
and the connected parts can be removed from the cylinder 4. 

1 Unless there is a very good reason for a change in the tension of 
the spring in the drum it should not be altered. Particularly in indicators 
which have been used a long time the pin holding the spring in place 
is likely to be much worn, so that if adjusted often the spring may get 
loose, and then there is often considerable difficulty in getting it again 
into its proper position. 




Fig. 81. — Section of Thompson Indicator. 



ENGINE INDICATORS AND REDUCING MOTIONS 



S9 



By unscrewing the spring by hand from the cap, which, of 
course, must be prevented from turning, and also from the screw 
on the swivel head 12, the piston, the spring and the hollow 
piston rod 10 are detached from the other parts. A socket- 
wrench of the special form provided in every indicator box of 
this make is to be slipped over the piston rod to engage with 
the small nut shown in Fig. 83 at the lower end of the piston rod 




Fig. 82. — Typical Crosby Indicator. 

10. Then the piston rod is readily unscrewed from the piston 
at the same time the spring in the indicator is released from 
its attachment to the piston. Now with the piston rod still 
in the socket of the wrench, slip the spring to be used over the 
piston rod until the head of the spring rests in the concave end 
of the rod. To do this, the wrench must be held upright, and 
then if the piston is inverted, or, in other words, if it is held 
so that the end screwing into the piston rod points downward the 
piston rod is ready to be screwed into the piston so that the trans- 



90 



POWER PLANT TESTING 



verse wire of the spring passing through the bead will be held 
firmly in the slotted portion of the socket in the piston. Finally 
screw the piston rod firmly 1 into place. Before the last opera- 
tion, the lower piston-screw (Fig. 84) should be loosed slightly, 
and afterward it should be screwed up lightly against the bead 
to prevent lost motion. It should not be screwed so tightly, 




Fig. 83. — Section of Crosby Indicator. 

however, as to prevent the bead from turning, otherwise the 
desirable qualities of the ball-joint for securing perfect alignment 
are lost. Now when the piston-rod spring and piston are 
again assembled, if the sleeve 3 and the pencil motion attached 

1 Special care should be taken when putting a spring into a Crosby 
indicator that the piston rod is screwed into its socket in the piston P 
(Fig. 84) as far as it will go; that is, until the extreme upper end of the 
socket a a is brought firmly against the bottom of the corresponding 
annular channel b b in the piston rod R. 



ENGINE INDICATORS AND REDUCING MOTIONS 



91 




Fig. 84. — Section 
of Crosby Indi- 
cator Spring and 
Piston. 



to it are held in an upright position, the hollow piston rod can 
be slipped over the threaded portion of the 
swivel head 11 until the threads on the 
upper end of the spring engage with those 
on the cap 2. Then the spring can be 
screwed securely into the cap 2. Then per- 
mit the cap to turn in the sleeve 3, and by 
still turning the spring, screw the piston rod 
on the swivel head 12, until the top of the 
rod is nearly flush with the shoulder on the 
swivel head. The piston and attached spring 
are now ready to be put into the cylinder by 
slipping the sleeve 3 into position and screw- 
ing down firmly the cap 2. 1 

The height of the pencil cannot be adjusted to change the 
position of the atmospheric line without removing the piston 
from the cylinder of the indicator. It must be done, however, 
by unscrewing the cap 2 from the cylinder and removing it 
together with the sleeve 3 and the pencil mechanism. By 
turning the cap clockwise, the swivel-head 11, and consequently 
also the atmospheric line is lowered. By turning in the opposite 
direction both are raised. Never try to make adjustments by 
• removing or loosening the pins or screws at the joints, 17, 18, 
19, 20 and 21. These joints should always be kept tight enough 
to prevent any lost motion, and occasionally they should be 
lubricated with refined porpoise oil of the kind usually supplied 
with indicators. 2 



1 Persons in charge of tests should always inspect indicators before 
the steam pressure is put on the springs to observe whether the cap has 
been screwed down firmly, and whether the pencil mechanism has been 
adjusted so as to give with a suitable spring a diagram of the proper 
height on the drum. 

2 Inexperienced testers often put the spring and piston into place 
by merely slipping on the sleeve 3 and without screwing down the cap 2. 
Then, as a result, when the steam pressure is put on the indicator 
the piston, spring and pencil mechanism are thrown off with a great 
deal of force, and some of these parts are sometimes completely de- 
molished. 

When using an indicator having the spring inside the cylinder 4 — and 
this is true particularly in the Crosby Indicator — all adjustments should 
be made before the steam is turned on the indicator, because the piston, 
spring and cap soon become very hot, and unless the parts are cooled, 
preferably by dipping into cold water, they are difficult to handle. 



92 



POWER PLANT TESTING 



The tension of the spring in the drum is changed very much 
more conveniently than in most other indicators. For high- 
speed engines the tension must be considerably greater than 
that required for those running at low speeds. The tension 
is adjusted by removing the drum (24) by a straight pull, and 




Fig. 85. — Crosby Outside- spring Indicator. 

turning the knurled nut at the top of the spring (31) after 
lifting it from its square seat. 

Crosby Outside- spring Indicator. Indicators with springs out- 
side the cylinder (Fig. 85), so that they are not subjected to high 
temperatures, are particularly desirable for use with engines using 
superheated steam. There are two principal advantages : (1) The 
spring can be changed without removing the piston, avoiding 
an operation often causing confusion and loss of time; (2) the 



ENGINE INDICATORS AND REDUCING MOTIONS 



93 



tension of the spring cannot be affected by exposure to very 
high temperatures. The spring can be changed when the thumb- 
screw at the top of the central spindle has been unscrewed. 

Star Brass Indicator — Navy Pattern. The indicator called 
the " Navy Pattern," manufactured by the Star Brass Co., is 
shown in Fig. 86. In general principles of construction it is 
like the Crosby indicator illustrated in Fig. 85. The most 
essential differ- 
ence is in the 
type of straight- 
line parallel mo- 
tion for the pencil 
lever. It will be 
observed that this 
is practically the 
same as that used- 
in the Thompson 
indicator (Fig.8o). 

Tabor Indica- 
tor. In the form 
in which it is now 
manufactured the 
Tabor indicator, 
Fig. 87, differs 
from indicators 
like the Crosby 
particularly in the 
means employed 
for producing a 
straight-line parallel motion for the pencil. This is accom- 
plished by the movement of a roller attached to the pencil 
lever in curved slots on the inside of the rectangular box-shaped 
part shown in the figure, attached to the cylinder cap. 

As regards the point of flexibility in the mechanism, this 
is not between the spring and the piston, but, more like the 
Thompson, is between the piston and the piston rod. Details 
of this construction are shown in Fig. 88. 

To Change the Spring. The cylinder cap must be first 
unscrewed, and then this cap, together with the piston, spring, 
and connected parts can be lifted from the cylinder of the 




Fig. 86. — Star Brass Indicator — Nav}^ Pattern 



94 



POWER PLANT TESTING 



indicator. By removing the small screw under the piston the 
latter can be unscrewed from the lower end of the spring. 
The other end of the spring can then be unscrewed from the 
cylinder cap. Another spring is put into the indicator by 
slipping it over the piston rod with the end stamped T upper- 




Fig. 87. — Tabor Indicator. 



most, screwing this end into the cylinder cap and screwing 
the piston to the lower end. The pencil mechanism must be 
moved downward until the piston rod enters the piston and 
the square shoulder enters the corresponding square socket 
in the piston. In this last operation care must be taken that 



ENGINE INDICATORS AND REDUCING MOTIONS 95 

the rod is firmly and accurately in the hole, and then the screw 
at the bottom of the piston should be firmly applied. 

To Change the Tension of the Spring in the Drum. The drum 
itself is first removed. Then after loosening the knurled nut 
on the central shaft and after the drum carriage has been 
lifted clear of the stops, the carriage can «be turned in the 




Fig. 88. — Section of a Tabor Indicator. 

required direction to secure the necessary tension and it can 
then be replaced by lowering into the stops. Care must be 
taken also that a firm grasp on the drum carriage is not 
lost, otherwise the spring will become uncoiled and probably 
also detached. 

Bachelder Indicator. Fig. 89 illustrates an engine indicator 
which is in many essential parts entirely different from the 



96 



POWER PLANT TESTING 



general type to which all those already described belong. It 
is so simple in construction that scarcely any description is 
necessary. The most radical difference is, however, in. the 
form of spring used. This is flat and is arranged with a movable 
fulcrum which can be adjusted to change the scale of the spring. 
Although a wide range is obtainable in this way, it has been 
found unsatisfactory to attempt to use the single spring for all 
the ranges from the highest pressures to low vacuums. On 




Fig. 89. — Bachelder Indicator. 

this account at least two springs, one for high and the other 
for low pressures, are usually supplied. 

Springs are changed by first removing the taper screw 
shown at the extreme right-hand side in the figure, and then 
after unscrewing a circular cap on the side of the cylinder the 
pin connecting the spring to the piston rod can be withdrawn 
with a small pliers or similar instrument. Usually before the 
spring can be withdrawn the thumbscrew attached to the 
movable fulcrum must be loosened. In the ordinary operation 
of the instrument the piston is not removed. 1 

1 When the spring is calibrated, the piston should be taken out so 



ENGINE INDICATORS AND REDUCING MOTIONS 97 

The spring on the drum is conical in form and is adjusted 
in practically the same way as in the Crosby Indicator. 

Precautions for Care of an Indicator. Unless an engine 
indicator is well taken care of, very soon it will be in a condition 
in which no reliance can be placed on results obtained with it. 
That the necessary precautions should be taken is all the more 
important, because it is one of the most expensive as well as 
the most delicate instruments used by an engineer in his 
ordinary practice. The following precautions are particularly 
important : 

i. Before an indicator is used all the working parts, espe- 
cially the piston, should be carefully cleaned. Then after a 
spring suitable for the pressure has been attached in its proper 
position and a little cylinder oil has been smeared in a thin 
coat on the working surface of the piston the parts should be 
replaced. Moving parts of the pencil mechanism should be 
oiled occasionally with watchmaker's or porpoise oil. 

2. Adjust the screw on the handle provided for moving 
the pencil so that when the pencil is sharp the application of 
the usual pressure on the handle will give a very fine line. 

3. Adjust the length of the indicator cord so that the drum 
will be neither too loose nor too tight; or in other words, so 
that the drum will not strike either of the stops when the engine 
is operating. On a small engine this is most easily tested by 
observing the card when the engine is on each of the dead- 
centers. If the card is either too long or too short the drum 
will not be moved in either case the required distance, and the 
indicator card will be correspondingly too short, therefore 
inaccurate. The cord used should be selected with care. It 
must be of such a quality as not to be stretched appreciably 
by the forces to which it is subjected. 

4. The atmospheric line should always be taken, preferably 
after the diagram has been made. It is drawn when the indicator 
cock is closed. By this order of procedure in tests, the diagram 
can be more easily taken exactly " on the signal." For calcu- 
lations the length of the diagram must always be measured on 
the atmospheric line or on a line parallel to it. The indicator 

that a little cylinder oil can be put on it. It is not so necessary when 
in use on a steam engine, as the oil in the steam will usually provide 
sufficient lubrication. 



98 POWER PLANT TESTING 

cock should be kept closed and the cord to the reducing motion 
should be unhooked except when a diagram is to be taken. 
When the cord is unhooked the drum should not be permitted 
to snap back against the stop. 

5. Immediately after a diagram has been taken it should 
be removed from the drum and examined. If there are unusual 
irregularities in the lines, unaccountable differences in the 
areas or in the lengths of different cards, the facts should be 
noted and the best efforts should be made to remedy the faults. 
Irregularities are usually due to stretching of the indicator 
cord, grit on the piston, lost motion in the working parts, 
usually inside the indicator cylinder, or excessive friction 
caused by overheating of the piston, particularly when used 
on gas engines. 

To correct these faults concerning the piston it must be 
removed from the cylinder and should then be carefully 
cleaned and lubricated again with cylinder oil. Before 
putting the piston and connected parts back into the indi- 
cator cylinder it should be observed whether or not all the 
parts are connected firmly and without lost motion. 1 

6. After a test, the indicator should be removed immediately 
from the engine, protecting the hands with waste or thick gloves 
to prevent burns. All the parts, especially those in the cylinder, 
should be thoroughly cleaned and then put together again without 
the spring, which should be put away with the other springs 
in a box provided for the indicator. An indicator should never 
be handled by taking hold of the drum, as usually it is fastened 
to the indicator by only a loose slipjoint, and this comes off 
easily. 

1 One of the causes of errors in results obtained with indicators not 
so readily detected is due to the pencil motion not being parallel to that 
of the piston in the indicator. A simple test for this is to draw an 
atmospheric line on a card placed on the drum. The card should be at 
least as wide as the height of the drum. Then after taking out the spring 
raise the pencil to the full height of the card by pressing lightly on the 
piston. This operation should be repeated several times at several 
points along the length of the card. To secure the best accuracy it is 
desirable to " block " the drum in each position. If the lines drawn 
are exactly perpendicular to the atmospheric lines there is no error in 
the pencil mechanism. If the test for perpendicularity is made by a 
triangle and straightedge, it should be done with the triangle first lying 
on one side and then on the other, to eliminate any inaccuracy in it. 
Often the triangles used by engineers are very inaccurate. 



ENGINE INDICATORS AND REDUCING MOTIONS 



99 



SPECIAL TYPES OF ENGINE INDICATORS 

Cooley-Hill Continuous Indicator. For many purposes of 
investigation it is very important to have continuous records 
showing the variations of the cycles in the operation of an 




Fig. 90. — Cooley-Hill Continuous Indicator. 

engine. Many devices have been used for this purpose, but as 
the motion was taken from the crank shaft there was no simple 
relation between points on these diagrams and the correspond- 
ing points in the stroke of the engine. Furthermore, because 
of the difficult relation, such cards could not be measured with 
a planimeter. Similar apparatus for the same purpose operated 
by an electric motor were open to the same objection. To 



100 



POWER TLANT TESTING 



overcome these difficulties a continuous indicator was developed 
in the Engineering Department of the University of Michigan 
in which the motion was proportional at every instant to the 
movement of the piston. "With a diagram obtained with this 
instrument it is not difficult to determine the dead-center follow- 
ing release, and the conventional indicator card for an engine is 

then readily obtained by turning 
the diagram for the complete 
cycle back on itself by folding 
the card or ribbon at this dead- 
center. If transparent paper is 
used, the complete diagram can 
be seen with all the points in 
their true relative positions as 
regards the movement of the pis- 
ton. The indicated horse power 
can then be readily calculated 
with the aid of a planimeter. 
This continuous indicator is illus- 




trated in Fig. 90. The indicator 
cylinder C, the piston, and the 
pencil motion may be of any 
standard make, as the collar M, 
for attaching the drum mechan- 
ism, is adjustable in size so that 
it can be fitted to indicator cylin- 
ders of different diameters. By 
this arrangement only one drum 
motion need be provided for 
using this indicator motion on a 
number of types of indicators 
such as would be required for use 
with steam engines, gas engines, 
ammonia compressors, etc. In 
this apparatus the drum D moves forward a given amount 
with every stroke of the engine. The indicator cord S is con- 
nected to the indicator reducing motion, and is driven by being 
connected in the usual way to the cross-head of the engine. 

The mechanism operating the drum motion is illustrated in 
Fig. 91. It consists essentially of two miter wheels B and C, 



Fig. 



91. — Details of Cooley-Hill 
Indicator. 



high-pressure air compressors, 



ENGINE INDICATORS AND REDUCING MOTIONS 101 

meshing with a similar wheel E, to which the pulley W, carrying 
the indicator cord, is attached. At the top of the wheel B and 
at the bottom of C are so-called silent ratchet clutches, a, a, 
each of which operates in only one direction to grip the collars 
concentric with the wheels B and C. Only one of these collars 
is shown in the figure. Both are rigidly attached to the central 
spindle J, carrying the indicator drum D (Fig. 90) . For example 
this central spindle is gripped by the ratchets a, a in the wheel 
B, during the "forward" stroke of the engine, and is released 
during the " back " stroke. The ratchet in the wheel C, on 
the other hand, grips this spindle during the " back " stroke 
and releases on the " forward " stroke. In this way the drum 
D is constantly moved on the spindle J in the same direction. 
Neither of the wheels B nor C is directly attached to the central 
spindle, and they can move it only when they move in the direc- 
tion in which they grip their ratchets a, a, engaging in the 
grooves g, g. 

The miter wheels B and C are connected to each other by 
means of a spiral spring enclosed in the casing D. This serves 
the function of the ordinary drum spring in the usual type 
of indicator- for bringing the drum and string back when the 
cross-head moves toward the indicator. 

Optical Indicators. The usual types of indicators operating 
with a piston are not suitable for engines running at much over 
400 revolutions per minute. For higher speeds optical indi- 
cators are used. These operate by the deflection of a beam of 
light from a mirror, the deflection being proportional at any 
instant to the pressure. When such a device is used on an 
engine successive indicator diagrams can be readily observed 
and compared by marking with a pencil the reflection upon a 
ground-glass plate, and if a photographic sensitive plate is 
exposed to the beam of light in the place of the ground glass, a 
permanent impression can be taken, showing at any instant the 
operation of the engine. Optical indicators are practically the 
only kind that can be used successfully for indicating the action 
of modern high-speed automobile engines. Every well-equipped 
automobile testing plant should be provided with one of these 
instruments. One of the simplest and best apparatus of this 
kind is illustrated in Fig. 92. The indicator is shown in the 
picture vertically above and connected to the head of the engine. 



102 



POWER PLANT TESTING 



Steam pressure is communicated to the instrument through the 
usual type of indicator cock supporting it. A system of levers 
shown (a simple reducing motion) serves for reducing the 
length of the stroke of the engine to a suitable size for such a 
small instrument. A glass mirror moved about a vertical axis 
by the motion transmitted from the cross-head and about a 
horizontal axis by the pressure in the engine cylinder, reflects a 



" ^^\ 




Fig. 92. — Perry's Optical Indicator. 



beam of light from a lamp upon a sheet of paper so that the 
indicator diagram can be traced. 

Details of the essential parts of this instrument are shown 
in Fig. 93. Through the indicator cock the pressure in the 
engine cylinder is communicated to the cored passages marked 
A, A. This pressure tilts the mirror B, attached to the thin 
steel diaphragm D. When, therefore, the mirror is still, a ray 
of reflected light will be seen as a bright spot on the screen ; but 
when moved both by the pressure and the motion of the cross- 
head the conventional indicator diagram is traced. It is very 



ENGINE INDICATORS AND REDUCING MOTIONS 



103 




interesting to watch the rapid change of shape of such diagrams 
as load, speed, pressure, cut-off, etc., are changed. With such 
an instrument these 
interesting phenome- 
na in engine operation 
can be illustrated on 
a ceiling to a large 
class of students. 

Another type of 
optical indicator in- 
tended particularly 
for high-speed auto- 
mobile engines is 
shown in Fig. 94. In 
this instrument the 
movement of the beam 
of light is produced by 

reflection from a small mirror M arranged to move in two 
distinct planes at right angles to each other. In one plane 

Ground Glass Plate 




Fig. 93. 



-Essential Parts of Perry's Optical 
Indicator. 




(o)l )|j — Acetylene Burner 
Fig. 94. — Section of a "Monograph" Optical Indicator. 

the movement of the piston is accurately reproduced, and in 
the other the movement is proportional to the pressure. Either 



104 



POWER PLANT TESTING 



of these movements or deflections of the mirror, taken alone, 
would cause the reflected beam of light to trace on the ground- 
glass plate a straight line; that due to the pressure being 
arranged to produce a straight vertical line and that due to 
the motion of the piston a straight horizontal line. But 
obviously the two movements taken together trace a diagram 
indicating at any instant the pressure in the engine cylinder 
for the corresponding position of the piston. A flexible shaft, 
attached at one end to the crank shaft of the engine, moves the 
disk A and with it the crank C, as well as the small lever L 
attached to it. The free end of this lever is arranged to turn 
the mirror M about a vertical axis by means of the small strut a, 
while the pressure exerted on the diaphragm D, as transmitted 
from the engine cylinder by the pipe P, moves the mirror about 
a horizontal axis by means of the strut b. In this apparatus 
the diaphragm takes the place of the piston and spring in the 
ordinary type of indicator. These diaphragms, like those used 
in pressure gages (see page 8) can be made of such thicknesses 
that a diagram of satisfactory size can be obtained for high or 
low pressures. When the diaphragms are carefully calibrated, 
a reasonable degree of accuracy can be expected. The relative 

motions of the 

Acetylene mirror {n tfae 

two planes are 
set in phase by 
adjusting the 
milled screw S, 
operating a small 
worm wheel ser- 
ving for chang- 
ing the angular 
position of the 
crank disk A, 
movement of the mirror about the vertical axis 
due to the pressure. Fig. 95 shows the 

A 




Fig. 



95- 



Top of Tripod Stand 



Monograph " Optical Indicator Ready for 
Attachment to Engine. 



to make the 

correspond with that 

apparatus as it would be set up for indicating an engine 

sample indicator card taken with this apparatus from a gasoline 

automobile engine is shown in Fig. 96. 

Calibration of Indicator Springs. The pistons of engine 
indicators are invariably made of a very definite area, usually 



ENGINE INDICATORS AND REDUCING MOTIONS 105 

one-half square inch ; and it is possible to calibrate the deflection 
of the springs with respect to this area, so that a certain definite 
pressure per square inch * in the cylinder will correspond to a 
definite deformation of the springs. In English units the pressure 
on the piston in pounds per square inch corresponding to a move- 
ment of the indicator pencil on the diagram of one inch is called 
the scale 2 of the spring. Indicator springs should always be 
calibrated by the makers. The calibration should be made 
when they are in the indicator in which they are to be used. 




Fig. 96. — Indicator Card taken from an Automobile Engine with Optical 
Indicator. 

Cooley Apparatus for the Calibration of Indicator Springs. 

An apparatus similar to the one designed by Professor M. E. 
Cooley of the University of Michigan is most generally used for 
the calibration of indicator springs. One of the latest and more 
elaborate forms of this instrument is shown in Fig. 97. In its 
essential parts this apparatus consists of a small cylinder C, sup- 
ported on a bracket B, a connection I, at the top of this cylinder 
for the attachment of the indicator to be tested, and a stuffing- 
box or gland at the bottom of the cylinder into which a plunger- 
piston P is fitted. The lower end of this plunger rests on a 
sensitive platform scales. Any pressure in the cylinder C can 
therefore be weighed. Steam is admitted to the cylinder through 

1 Indicators are always designed to relieve the pressure above the 
piston due to leakage around it, so that on this side there is always atmos- 
pheric pressure. 

2 Instead of " scale " the word " number is often used. That is, 
a spring of which the scale is 40 pounds would be called " No. 40." 



106 



POWER PLANT TESTING 



a pipe E, and is exhausted through the pipe A. By adjusting the 
globe valves on the pipes A and E any pressure desired can be 
secured in the cylinder C, and this same pressure is, of course, 
exerted both on the piston of the indicator above and on the 
plunger P below. This plunger is usually made with an area of 
one-half square inch. For a plunger of this area, then, if for a 
given pressure the scales balance at 10 pounds, the pressure in 
the cylinder C, and on the piston of the indicator, is 20 pounds 




Fig. 97. — Apparatus for Calibrating Indicator Springs. 

per square inch. To eliminate friction as much as possible, 
the plunger P should be kept spinning when observations are 
being taken. For this purpose a hand wheel K with considerable 
mass, for its " fly-wheel " effect, is provided on the shaft of the 
plunger. A more uniform motion of the plunger is obtained, 
however, by having the hand wheel grooved to take a small 
belt to be driven by an electric motor M. The plunger is sup- 
ported usually on a ball-bearing joint set in a low pedestal L. 

By connecting a pipe E to a suitable manifold or similar 
fitting, to which are attached three separate pipes supplying 
respectively steam, air, and water under pressure, an indicator 



ENGINE INDICATORS AND REDUCING MOTIONS 



107 



can be tested with varying pressures under the actual conditions 
in service; that is, when used for steam, air or water. 

A simpler form of the Cooley apparatus intended for the 
so-called "dry method" of testing is shown in Fig. 99. A 




Fig. 99. — Apparatus for "Dry" Method of Indicator Testing. 



suitable fitting for receiving the ind cator I is supported on the 
bracket B. The legs of this bracket span over a sensitive plat- 
form scales S. A small rod R rests at its lower end on a small 
pedestal standing on the platform of the scales S. On the top 
of this rod there is a cap supported on a small conical bearing to 



108 POWER PLANT TESTING 

give some flexibility. This cap is made to fit easily into the 
lower side of the piston in the indicator. The indicator itself is 
attached to the top of the hand wheel W. Then when the hand 
wheel is screwed downward the indicator comes down with it 
and compresses the indicator spring. At the same time a pres- 
sure is exerted on the rod R which can be balanced on the scale 
beam. When a force is applied to compress the spring in the 
indicator, the magnitude of the force can be determined by 
weighing the pressure on the scales. If the area of the piston 
in the indicator is one-half square inch, then twice the weight 
on the scales is the pressure exerted in pounds per square inch. 
Heat can be applied to the indicator by passing steam through 
a rubber tube wrapped around the cylinder. 

Method for Calibration of Springs. After cleaning the 
internal parts of the indicator, inserting the spring to be cali- 
brated, and oiling the piston with cylinder oil, the indicator 
is to be attached to the indicator cock on the calibrating appara- 
tus. Before putting the card on the indicator drum on which 
the record is to be made, two approximately parallel and vertical 
lines should be drawn on it about one-half inch apart, similar 
to the lines AB and CD in Fig. ioo. Meanwhile the indicator 
should be thoroughly warmed if a calibration with steam 
pressure is to be made. Then with the indicator cock and the 
valve on the steam pipe E closed and the one on the exhaust 
pipe A open, draw the first calibration line on the card. This 
should be made by setting the pencil point at D, and then by 
pulling the cord attached to the drum draw a line crossing 
the vertical line AB. With springs of which the scale is 30 
pounds or less, a similar record should be made for incre- 
ments of every 5 pounds per square inch change in pressure, 
while for higher scales the increments may be made 10 pounds. 
If with increasing pressures the lines are drawn toward the 
left, then with decreasing pressures they should be drawn toward 
the right with equal increments, beginning at the opposite 
vertical line AB. By this method the corresponding lines for 
equal pressures will be immediately over each other between the 
two verticals. With an accurate scale, graduated preferably 
to one one-hundredths inch, measure between AB and CD the 
distance from the atmospheric line first drawn to the various 
''pressure lines, "and record the results. Care should be taken 



ENGINE INDICATORS AND REDUCING MOTIONS 



109 



that with the increasing increments the pencil rises to the 
required pressure and that with decreasing increments it falls 
to these pressures. In other words, if when the lines for 
increasing pressures are being drawn, the pressure rises too 
rapidly to draw the line at the proper time when the scale 
beam is just balancing, then the pressure should be again 
reduced below the value required, so that the pencil will be again 
ascending when the line is drawn. Similarly for decreasing 
pressures, if the pressure gets too low, it must be increased and 
again brought down to the required value. 1 If the results 



No_£ Hour. / '. T #-?IVL 

Which End 

B. Press 

Vac. gauge.. ~ 

Revs. 

Spring 



Up 



INDICATOR NO. 



c 



Area 

Length- 
M. Orri\. 
M.E.P.. 

i.h.p_. 



—"Atmospheric" Lines 
D OBSERVER 



Fig. ioo. — Sample Card Illustrating a Test of an Indicator Spring. 



obtained do not seem to be consistent, the difficulty is probably 
due to passing the required pressure so rapidly that the lines 
have not all been drawn at the proper time. 

The difference between the lines for increasing and decreasing 
pressures shows the amount of friction and lost motion in the 
indicator. 2 The error of the instrument is obtained by comparing 
the mean ordinates of the card thus obtained with the actual 

1 The same precaution must be observed in beginning the test. To 
be sure that the pencil and piston have not been falling instead of rising, 
the piston rod should be pushed down lightly before the atmospheric 
line is drawn. 

2 Half of this difference, to be more accurate, represents the friction 
and lost motion in that position. 



110 



POWER PLANT TESTING 



pressures as determined by weighing. From time to time the 
accuracy of the platform scales should be determined by test- 
ing with standard weights. For dependable results two cali- 
brations, each "up and down,'^ should be made for each spring 
and the results compared. 

When indicators are used for pressures which are never 
less than atmospheric, the springs are in compression and appa- 
ratus of the form 
described are satis- 
factory ; but when 
indicators are used 
on the low-pressure 
cylinders of engines 
the springs are 
usually in tension. 
For this service a 
slightly different de- 
vice must be used 
for calibration. A 
suitable apparatus is 
shown in Fig. 101. 

The indicator I 
is supported on a 
bracket similar to 
the one used in the 
apparatus shown in 
Fig. 99. A short 
steel rod (about No. 
18, B. & S. gage) 
is attached to the 
lower side of the 
piston in the indicator by screwing into a hole tapped centrally. 
Now if weights are suspended from the end of this rod * the 
spring can be calibrated in tension by drawing lines on a paper 

1 The weight of this rod and wires or strings supporting the weights 
must be added to them to get the correct tension. If, however, only 
the true scale of the spring is desired, as is usually the case, the weight 
of these parts need not be considered, provided, of course, the atmos- 
pheric as well as the other lines are all drawn with these parts attached 
to the piston. 




Fig. i 01. — Apparatus for Testing Indicator 
Springs in Tension. 



ENGINE INDICATORS AND REDUCING MOTIONS 111 



card placed on the drum in the same general way as when the 
spring was tested in compression. 

A suggested form for the arrangement of data for these 
calibrations is given below. 

Calibration of Indicator Spring (Compression) 

In Indicator No 

Rated scale of spring 

Diameter of piston of testing apparatus ins. 

Area of piston of testing apparatus . . . : sq.ins. 

Identification marks on spring 



Observers 



Date. 



No. of 


Weight 

on 
Scales, 
Lbs. 


Actual 

Pressure 

on 

Piston, 
lbs./sq.in. 


Ordinates or " Heights " 
Measured on Card, Inches. 


True 
Scale of 
Spring, 
(3) -H6). 






Up. 


Down. 


Average. 


Remarks. 


i 


2 


3 


4 


5 


6 





















Curves. Results should be shown graphically for calibra- 
tions of indicator springs by plotting for abscissas the average 
height, inches, and for ordinates the corresponding actual 
pressures in pounds per square inch. 

Calibration of Indicator Springs with the Mercury Column. 
The method to be followed in calibrating indicator springs 
with a mercury column is essentially the same as described on 
pages 18-22 for the calibration of pressure gages. After the 
indicator has been cleaned and oiled, it should be attached to 
the testing drum or cylinder by means of an indicator cock. 
Then while the indicator is being heated to the temperature of 
the fluid medium used (steam, air, or water), the paper card 
can be put on the drum after first drawing two vertical lines 
one-half inch apart, as explained when describing the Cooley 
apparatus. Following these same instructions the atmospheric 
and other pressure lines are drawn first with increasing and then 
with decreasing increments. 



112 



POWER PLANT TESTINCx 



Testing the Drum Motion of Indicators. An apparatus 
for determining the relative accuracy of the drum motion of 
indicators as regards uniform tension in the cord for a given 
speed is illustrated in Fig. 102. This device, known as Brown's, 



®=S 



B 



Fig. 



—Brown's Apparatus for Testing Drum Motion. 

consists of a rod R, which is made to take the same movement 
as the end of the cord in a reducing motion by being attached 
through a connecting rod to a crank pin on a disk like the face 
plate of a lathe. At the other end this reciprocating rod is 
attached to a bell-crank lever F, of which the outer end P 
carries a pencil for making a diagram on a card attached to a 
vertical frame 0. 

The short end A of the bell-crank is connected to a helical 
spring S and the other end of this spring is attached to an arm 
fitted on the rod R. To the end of the spring at A the indicator 




Fig. 103. — Diagrams taken from Apparatus for Testing Drum Motion. 

cord is attached, being of the same length as when in use on an 
engine. Now when the reciprocating rod R is in motion and 
the tension in the spring S is uniform the pencil at P will describe 
a horizontal line. If, however, the tension in the indicator 
cord varies and consequently also the tension in the spring is 
not uniform, the pencil will describe a closed curve. Examples 



ENGINE INDICATORS AND REDUCING MOTIONS 



113 



»Cord to Indicator 



of such curves are shown in Fig. 103. Curve AB was obtained 
when the apparatus was moving very slowly, EF when operating 
at about 700 revolutions 
per minute, and CD 
when the speed was 
about 2 50 revolutions 
per minute. The latter 
speed is obviously the 
one for which the stiff- 
ness and length of the 
spring in the indicator 
drum are most suitable. 
Reducing Motions for 
Indicators. In the case 
of most engines the 
length of the stroke is 
very much longer than 
the greatest possible 
movement of the drum 
of the indicator. It 

is therefore necessary to provide some means called a reducing 
motion, which produces shorter movement, but which at every 



Cord to 
Indicator 




Fig. 104. 



-Simple Pendulum Reducing 
Motion. 




Fig. 105. — Pendulum and Quadrant Reducing Motion. 

instant corresponds exactly with that of the cross-head. If 
this correspondence is not secured the length of the indicator 



114 



POWER PLANT TESTING 



diagram cannot be accurately reduced nor calculated, and the 
timing of the events or so-called " points in the stroke " will 
not be correctly represented. 

One of the simplest forms of reducing motions is illustrated 
in Fig. 104. This device is pivoted at one point A to a pedestal 




Brumbo's Pulley. 



supported on the frame of the engine, and has a link BH con- 
nected to the cross-head. The indicator cord rides in a circular 
arc CD, proportioned to give the required movement to the 
drum of the indicator. Although this arrangement does not 
give an exact reproduction of the movement of the cross-head, 
yet if the pendulum AB and the cross-head are simultaneously 



ENGINE INDICATORS AND REDUCING MOTIONS 



115 



at the middle of their strokes the error is insignificant. An 
improved type of this device is shown in Fig. 105, in which the 
cord rides in a groove on the circumference of a quadrant 
pulley. By attaching the pendulum to the quadrant pulley by 
means of a suitably designed "slip" joint, the pendulum can 
be disconnected from the quadrant so that the indicator cord 
will be moved only when the indicator diagrams are to be 
taken. 




Fig. 107. — Pantograph or Lazy-tongs Reducing Motion. 



Brumbo's Pulley is also a form of reducing motion of the 
pendulum type. It is illustrated in Fig. 106. In this device 
a guide pulley is placed between the indicator and the quadrant 
pulley. A modified and simpler device of the same kind consists 
of an upper portion moving in a vertical direction in a swinging 
tube and a lower portion pivoted directly to the cross-head. 

Of the portable devices used for reducing motions the pan- 
tograph, Fig. 107, is probably the one most used. This device 



116 



POWER PLANT TESTING 



is sometimes known as a lazy-tongs. Because of the numerous 
parts of which it is composed, requiring a great number of joints, 
it is likely to be troublesome with high-speed engines. A plan 
view showing one of the methods of attachment of this device 
to a horizontal engine is given in Fig. 108. This instrument 
when firmly put together is a perfect reducing motion. 



Fig. 




Plan View, Showing Attachment of Pantograph. 



Parallel Motions, like the one illustrated in Fig. 109, are also 
very commonly used. They are made usually of rods of iron or 
of steel nicely riveted together at the joints. The indicator cord 
is generally attached at B and the ends A and C of the long rod are 




Fig. 109. — Simple Parallel 
Reducing Motion. 



Fig. 1 10. — Simple Parallel Reducing Motion 
as Attached to a Steam Engine. 



fastened respectively to the cross-head and to the frame of the 
engine. It is a necessary requisite that the points A, B, and C 
shall lie in a straight line as shown. Also DE must be equal 
in length and parallel to FG. Then AF is in the same ratio 



ENGINE INDICATORS AND REDUCING MOTIONS 117 



to HF as the stroke of the piston is to the length of the indica- 
tor diagram. 

Methods of attachment of similar devices to engines are 
shown in Figs, no and in. 




Fig. hi. 



-Simple Parallel Reducing Motion as Attached to an Air 
Compressor. 



Fig. ii2 illustrates another interesting parallel motion. 
It consists of a rod R, moving in a slide S, parallel to the piston- 
rod. A link BD is attached to the slide R at B and to CE at D, 
while AE is fastened 
at one end to the 
cross-head C. In this 
case again if A, B, 
and C are in the 
same straight line, 
then the following 
relation holds: AE : 
BD and CE : CD as 
the stroke of the 
piston is to the 
length of indicator 
diagram. The cord 
is hooked on a pin 
at H. It is desirable to have 
cator used. 

Reducing Wheels which consist simply of a large and a small 
pulley attached to the same axis, are coming into more or less 
general use. A typical arrangement is illustrated in Fig. 113. 
Pulleys D and D' are usually connected by a sliding sleeve so 




Fig. 112. — Sliding Type of Parallel Reducing 
Motion. 



a separate pin for each indi- 



118 



POWER PLANT TESTING 



that they can be disconnected when indicator diagrams are not 
being taken. 

Fig. 1 14 is a device by Armand Stevart for engines with long 
strokes. A and B are fixed ends of cord wrapped around a 





Fig. 



Fig. 113. — Reducing Motion of Concentric Pulleys. 

pulley D. The indicator cord g is attached to a small pulley D' 
and passes around a guide pulley G. D and D' are attached 
to the cross-head C. Then diameter D-=- diameter D' = stroke of 
piston-^- by the difference between 
stroke of piston and length of card. 
Reducing Wheels are not infre- 
quently made for attachment di- 
rectly to the indicator, as illustrated 
in Figs. 115 and 116. The former 
shows the Crosby reducing -wheel 
attachment and the latter a similar 
device for the Tabor indicator. 

Calculations of the Indicated 
Horse Power of an engine show 
usually the power developed on one side of the piston, which is 
commonly stated by the formula, 

I.H.P.^Pi^. ..... 

33,000 

Where p= mean effective pressure on the piston, lbs. per sq. in.; 
1 = length of stroke in feet; 
a=net area of piston in square inches; 1 
n=number of revolutions per minute. 

x In all piston engines the area of the piston rod must be subtracted 
from the area of the piston on the side where the rod reduces the area 
effective for the action of the steam or other working substance. 



1 14. — Armand Stewart's 
Reducing Motion. 



(*S) 



ENGINE INDICATORS AND REDUCING MOTIONS 



119 



Of the terms of this equation only one, the mean effective 
pressure, is obtained from the indicator cards. 

If we consider now only one end of the cylinder, the steam 
does work on the piston during a " forward " stroke, and, on 
the other hand, the piston does work on the steam on the 
" return " stroke. Hence to get the mean effective pressure 
for a stroke the average pressure during the return stroke must 
be subtracted from the 
average pressure on the 
"forward " stroke; and 
this is ob viou sly the same 
as the average length of 
all the ordinates inter- 
cepted between the u pper 
and lower lines of the 
indicator card multi- 
plied by the scale of the 
spring. 

Usually the mean 
effective pressure is 
found by means of plan- 
imeters, the use of which 
for this purpose was ex- 
plained on pages 72- 
77. An engineer should, 
however, know how 
to calculate the mean 
effective pressure of an 
indicator diagram with 
reasonable accuracy 
without the use of 
such instruments. In 

such cases the method of ordinates is very convenient. With 
suitable triangles draw ordinates perpendicular to the atmos- 
pheric line at both ends of the diagram as shown in Fig. 117. 
Lay off on the edge AB of a piece of smooth flat paper, a scale 
of ten equal divisions so chosen that the total length of the 
ten divisions is a little greater than the length of any of the 
indicator diagrams. This scale should then be placed obliquely 
across the diagram to be measured, so that the beginning and 




-Crosby Indicator and Reducing 
Motion Attachment. 



120 



POWER PLANT TESTING 



end of the scale will be located on the ordinates at the ends of 
the diagram. Now mark the diagram opposite the divisions 
of the scale with fine points, and at the middle of each of these 




Fig. i i 6. —Reducing Motion Attachment for Tabor Indicator. 

divisions draw ordinates across the breadth of the diagram. 
The sum of the lengths of these ordinates divided by ten gives 
the value of the mean ordinate, and this when multiplied by 



Fig. 




Diagram Illustrating Method of Mean Ordinates. 



the true scale of the spring gives the mean effective pressure. 
Some time can be saved in summing the ordinates if they are 
transferred with a dividers one after the other to the edge of 
the strip of paper. The total length laid off divided by ten is 
then the mean ordinate. 



ENGINE INDICATORS AND REDUCING MOTIONS 121 

The Engine Constant for Indicated Horse Power. In the 

use of equation (25), page 118, where 

I.H.P.= Pi^, 
33,ooo 

considerable time can usually be saved when calculating engine 
tests if the terms 

la / a\ 

, . ..... (26) 

33,ooo' 

called the engine constant, which always remain constant for each 
end of the cylinder, are first computed carefully and then used 
as constants throughout the calculations. In other words, the 
indicated horse power is found for each end of the cylinder by 
taking the product of the terms, 

Engine Constant XpXn. 



CHAPTER VI 

MEASUREMENT OF POWER— DYNAMOMETERS 

A dynamometer, according to its derivation, is an instrument 
for measuring force or " power." These are of two kinds: 

i. Those absorbing the power by friction and dissipating it 
as heat. 

2. Those transmitting or passing on the power they measure, 
thus wasting only a small part in friction. 

Absorption Dynamometers (Prony Brakes). Of the class 
of dynamometers in which the power received is all absorbed 




Fig. i i 8. — Simple Prony Brake. 

in friction, the type generally used is called a Prony brake, 
named for Rev. John Prony, who many years ago developed 
a device of this kind for measuring power. 1 One of the simplest 
forms is shown in Fig. 118. 

It consists of a lever A, from which a weight w is suspended 
from one end, and a block B, supported on a revolving drum or 
pulley, is attached to the other end. A strap to which wooden 
cleats are fastened is held in place and tightened by the thumb- 
nuts N, N. When the friction on the strap and block just 



1 Strictly speaking, a brake of this kind does not provide means for 
directly measuring power, as, for example, horse power, because the 
element of time is not indicated. In other words, it measures the 
tangential force of which a couple (torque) in linear-weight units, such 
as foot-pounds, can be computed. 

122 



MEASUREMENT OF POWER— DYNAMOMETERS 123 

balances the weight w, the lever arm A is horizontal and the 
apparatus is in adjustment. Stops, marked S, S, are provided 
so as to limit the movement of the lever arm. 

When the brake is adjusted or " balanced," the work done 
in a given time in producing the friction (the power absorbed) 
is measured by the weight moved multiplied by the distance 
it would pass through in that time if free to move. Then if, 
r= length of brake arm in feet. 1 
n = revolutions of the shaft per minute. 
w = weight on the brake arm in pounds. 

Brake Horse-power (B.H.P.) = . . . (27) 

33,000 " 

2irr 

In equation (27) the fraction is a constant quantity 

33,ooo 

for a given brake and is called 1he brake constant. When a brake 
like the one in Fig. 118 is used the effective weight of the brake 
itself as weighed at the point P must be added to the weight w. 
A very common variation 2 of the Prony brake is illustrated in 
Fig. 119. Rotation being in the opposite direction from that in 
Fig. 118, the knife-edge at E on the arm A will now press on 
the pedestal T, and the weight w can be determined by 
weighing the pressure on a platform-scales S. Since the 
scales receives not only the pressure due to the force pro- 
ducing friction, but also that due to the weights of the 
brake and of the pedestal, these weights must be determined 
and are to be subtracted from all of the readings of the 
scales to obtain the net weight w, for substitution in equation 
(27). Weight of the brake and the pedestal, called the zero 
reading, must be obtained with the brake strap slack, so that 
the block B will rest as lightly as possible on the pulley. 
With small engines this zero reading is obtained most 



1 The length of the brake arm is measured by the perpendicular 
distance from the line of action of the weight w to the center of the 
wheel. When the arm A is horizontal, as in Fig. 118, the length of 
the brake arm is usually measured by the horizontal distance from P to 
a line passing through the center of rotation perpendicular to the arm. 

2 For information regarding the designing of Prony brakes for absorb- 
ing large powers the reader is referred to Engine and Boiler Trials, by 
R. H. Thurston, pages 360-279. 



124 



POWER PLANT TESTING 



accurately by observing the weights on the scales when 
the brake pulley is turned around by hand first in one 
direction and then in the other. In this way we obtain for 
both the brake and pedestal, with rotation in one direction the 
weight plus the friction due to their own weight, and with rota- 
tion in the other direction the same weight minus the same 
friction. Half the sum of the two readings is, therefore, the 
weight corresponding to the pressure on the scales due to 
gravity alone. With large engines it 4s sometimes difficult to 
turn them uniformly by hand, so that the zero reading must be 
obtained by some other method. This is done usually in prac- 





Fig. 



-Prony Brake with Platform Scales. 



tice by placing a very small rod on the drum or pulley D (Figs. 
118 and 119) vertically over the center of the shaft. Then if 
the strap is loose and due care is observed, the pressure on the 
scales can be obtained with sufficient accuracy without rotation. 

Other forms of Prony brakes are illustrated in Figs. 120 
and 121. The former is called a strap brake and the latter 
a rope brake. 

The strap brake is made up merely of a band of steel or 
leather or of strands of rope placed over or wrapped around a 
suitable pulley. 1 In this case weights must be suspended from 
both sides of the brake wheel or pulley. 



1 It is desirable to use for Prony brakes pulleys of which the section 
of the face is a double " U," like Fig. 122. The outside rims are 
for keeping the brake in position on the pulley and those on the 



MEASUREMENT OF POWER—DYNAMOMETERS 



125 



Rope brakes x like the one shown in Fig. 121, are much used 
for "commercial testing" of engines, as it is easily portable or 
can be made quickly at a small expense from materials always 
at hand. Moreover, it is self-adjusting, so that accurate fitting 
is not required. It consists of a rope doubled around a pulley 
or fly-wheel on the shaft 
transmitting the power to 
be measured. Several U- 
shaped distance pieces of 
wood, preferably maple, 
are provided to prevent 
the rope from slipping 
off the pulley and to keep 
the parts of the rope 
separated. These dis- 
tance pieces should be 
attached to the rope by 
soft iron or copper belt 
lacing, drawn in from the 
outside of the wooden 
pieces through the center 
of the rope, instead of 
being fastened with screws or nails on the inside, which will 
heat to a high temperature and then char the rope. Sometimes 
such fastenings when of hard metal will cut grooves into the 
surface of the pulley. 

In the case of the strap brake, Fig. 120, the net pull, cor- 
responding to the weight w, inequation (27), page 123, is Wi — W2. 
inside for receiving a small stream of water played upon the inside of 
the pulley. This stream of water by its evaporation will assist materi- 
ally to dissipate the heat generated. Such brakes are often operated 
with pipes arranged to discharge water into the pulley and another pipe 
to carry it away. This is an excellent system provided the latter pipe 
is used only to carry away a little overflow, but if so much water is used 
that there is practically no " steaming," the inside rim of the pulley 
will fill up with water to be spattered around in every direction as well 
as over the face of the pulley, where it is particularly objectionable, as 
it produces variable friction. 

1 Sir William Thomson (Lord Kelvin) invented in 1872 the first 
rope brake of which we have any record. Although he utilized this 
device as a friction brake, it was not used by him as a dynamometer. 




Fig. 120. 



126 



POWER PLANT TESTING 



Now the same relation would hold if, as is often done, a spring 
balance is fastened to the floor on say the left-hand side; the 
pull registered by the spring balance would then be Wi 1 , and 
the net pull is, as before, W1-W2. Brake horse power is cal- 
culated then by equation (27), substituting for w the net pull 



<?S/sr/////////7////////y//S??^ 




FiCx. 121. — Rope Brake. 

Wi- Wo. The same is true also for the rope brake in Fig. 121 
so that for these two dynamometers we have 

2irrn(wi — W2) 



Brake Horse Power (B.H.P.) 



(28) 



33,ooo 

1 To the pull (wj) must be added, however, the weight of any hooks 
placed between the end of the strap or rope and the spring balance ; and 
if the balance is for any reason suspended in the inverted position the 
weight of the balance itself must also be added. 



MEASUREMENT OF POWER— DYNAMOMETERS 



127 



Where r is the radius of the wheel plus one-half the diameter 
of the rope in feet, and n is the revolutions of the shaft per minute. 

Alden Brake. An entirely different type of absorption 
dynamometer is the Alden brake, which is illustrated in Fig. 123. 

In this apparatus the rubbing surfaces producing the friction 
necessary for absorbing the power are separated by a film of 
oil, and the heat generated is carried off by a stream of water 
circulating through it. It consists of a disk of cast-iron A, which 
is to be connected to the shaft S, transmitting the power. 
This disk revolves between two thin copper plates E, E, fastened 
together at their outer edges to form a shallow cylinder which 




Fig. 122. — Brake Pulley. 



is filled with a bath of heavy (cylinder) oil. Water under 
pressure is discharged into the chamber adjoining the copper, 
plates and any increase in pressure causes the copper plates 
to press against the cast-iron plate A with more force. The 
friction between these copper and iron plates tends to turn 
those of copper, but as these are rigidly connected to the out- 
side casing C, carrying the brake arm P, the tendency to turn 
can be determined by weighing as with a Prony brake. To 
maintain the moment of resistance constant under all circum- 
stances the pressure and consequently the flow of water into 
the casing is automatically regulated by a cylindrical valve 
V, which becomes partially closed if the brake arm moves above 
a certain horizontal position. This valve is shown in section 



128 



POWER PLANT TESTING 



in Fig. 124. The end at W is connected to the water main 
and the other end Y to the brake casing by means of a right- 
angled bend R (Fig. 123). Water entering by the pipe W 
passes through the ports N and then through the ports H into 
the pipe Y. Now a small angular movement of the pipe W, 
relative to the pipe Y, will open or close the ports H and thus 
regulate the supply of water. These ports are very narrow, 




Fig. 123. — Alden Brake. 

so that a very small angular motion is sufficient to close them. 
By making the outer casing of the valve of rubber it is found to 
be sufficiently flexible to permit moving the valves, and at the 
same time it offers very little resistance to the movement of the 
casing. 

Water Brakes. Power is absorbed by moving, in water, a 
rotor similar in most cases to those in steam turbines. Such an 
apparatus is called a water brake. A good example is shown 
in Figs. 125 and 126. 

It is the type used by the Westinghouse Machine Company 



MEASUREMENT OF POWER— DYNAMOMETERS 



129 



of Pittsburg for testing the power of large steam turbines. It 
consists of a rotor R, mounted on a shaft S, S, of which one end 
is arranged to be connected directly by means ol a coupling 
to the shaft of the turbine or engine to be tested. This rotor 
revolves within a closed casing Z, supported on the journals 
J, J, through which the shaft passes. Around the periphery 
of the rotor there is a series of rows of vanes which when 
revolving tend to give to any water contained in the casing a 




Fig. 124. — Regulating Valve in Alden Brake. 

rotary motion. Between every two rows of vanes on the rotor 
there is fitted a row of stationary vanes attached to the inside 
of the casing. This arrangement is illustrated diagrammatic- 
ally in Fig. 126, where the cross-hatched sections represent the 
stationary vanes and the " solid " sections the moving vanes. 
The tendency of the moving vanes to produce this rotary 
motion of the water is, as it were, resisted by the stationary 
ones, and this action develops a very large amount of heating, 
due to fluid friction in a manner analogous to the operation of 
a Prony brake or any other absorption dynamometer. As a 



130 



POWER PLANT TESTING 



result of this friction a force is developed tending to turn the 
casing in the direction of motion of the rotor. The casing, 
however, is prevented from turning by a radial arm bearing 
down on a platform scales. The intensity of this tendency 




Fig. 125. — Westinghouse Water Brake. 

to turn can be regulated as in the Alden brake (page 127) by 
adjusting the valves controlling the flow of water through the 
casing. The vanes on the rotor are of the same kind as used 
in steam turbines and have the function of imparting a high 




Vanes of Westinghouse Water Brake. 



velocity to the water flowing through them in an axial direction. 
Water enters the casing through the inlet pipes C, C (Fig. 125), 
discharging a stream from both sides of the casing toward the 
central portion of the rotor. At the middle of the periphery of 



MEASUREMENT OF POWER— DYNAMOMETERS 131 

the rotor there are a number of slots or ports A, A, A, A through 
which the water discharges into the right and left, passing first 
through a broad central row of stationary vanes shown in Fig. 
126. Escaping from these vanes it is picked up by the rows 
of moving vanes on each side, which give it a high velocity and, 
in turn, discharge it into the adjacent rows of stationary vanes 
where the velocity just acquired is checked, and so on across 
the face of the rotor, the moving vanes adding velocity only 
to be lost in the next row of stationary vanes. From the last 
rows of moving blades the water is discharged into semicircular 
passages B, B', which direct the flow of water into the center of 
the rotor when the cycle is repeated. The water brake illustrated 
here was designed for high powers, so that a number of rows 
of vanes was necessary. For small powers of, for example, 
200 to 500 horse power, not more than two rows of moving vanes 
with the corresponding number of stationary vanes would be 
required. 1 

Power absorbed by a water brake is calculated in the same 
way as for an ordinary Prony or rope brake. 

In the operation of the brake the water is quickly raised 
to the boiling-point and a considerable portion evaporates, 
carrying off as steam very large quantities of heat. Vents for 
the escape of this steam are indicated in the figure, showing 
the cross-section of the brake by D and D'. Unless consider- 
ably more water, however, was admitted to the casing than was 
required to replace that lost by evaporation, the action of the 
brake would be more or less irregular, so that an excess of water 
is supplied and there is a constant discharge of hot water 
through the passages marked E and E'. 

Dynamos (Electric Generators and Motors) as Power Dyna- 
mometers. One of the most convenient means for measuring 
the power of high-speed engines and turbines is to connect an 
electric generator to the main shaft. Then if the efficiency of 
the generator is known at the particular speed and output at 
which it is to be operated, a very accurate method of meas- 
uring the power of the engine or of any other type of motor 
becomes readily available. The output of the generator 
should be determined by observations of the volts and 

1 To calculate the resistance of such vanes see " The Steam Turbine," 
by the author, pages 1 15-125. 



132 POWER PLANT TESTING 

amperes with carefully calibrated portable instruments. Re- 
membering that for direct-current generators volts times 
amperes gives watts and that 746 watts are equivalent to one 
horse power, then if E.H.P. is the horse-power output of the 
generator we have, 

pnn volts X amperes 

xL.xi.r\ = 7 . 

746 

It is not unusual to hear this result called the " Electrical " 
horse power. 1 

The actual horse power delivered to the generator is, of 
course, the brake horse power, and into this result the efficiency 
of the generator enters. Thus, 

B H _ volts X amperes 

746 X efficiency of generator" 

As a rule, however, electric motors are more serviceable in 
mechanical engineering laboratories as power dynamometers, 
because the efficiency is much more easily obtained, the usual 
method being to determine an efficiency curve for varying power 
inputs by a Prony brake test, stating this efficiency as, 

D Tip 

Efficiency of motor = ' ' t 7 : > 
Ji.Ji.P. 

where E.H.P. is the " electrical " horse-power input, as meas- 
ured with voltmeter and ammeter. 

If then a pump, air compressor, ventilating fan or a similar 
machine is to be tested by the electrical method, it should be 
direct-connected to the shaft of the motor, and its efficiency, 
E, will be 

E U-H.P. 

E.H.P X efficiency of motor' 

where U.H.P. is the useful work done by the machine, in 
horse power. 

1 When an alternating-current generator is used the power factor 
must also be measured with a suitable instrument. In this case, the 
actual E.H.P. is (volts X amperes X power factor) + 746. This method 
is discussed more in detail on pages 293-295. 



MEASUREMENT OF POWER— DYNAMOMETERS 



133 



This last method serves also as a convenient method for 
obtaining the efficiency of a generator, since by connecting it 
directly to the shaft of a motor previously " calibrated " (for 
efficiency) the electrical output of the generator and the input 
to the motor are readily determined. 

When a so-called variable speed motor is used as a dyna- 
mometer, its efficiency must be determined at the particular 
speed and power at which it will operate when driving the 
machine to be tested. 

Transmission Dynamometers. Instruments of this type 
are used to measure the amount of power transmitted without 

absorbing any more power 

than is absolutely needed to 
move the dynamometer. 

Goss Belt Dynamometer. 
One of the simplest forms of 
transmission dynamometers, 
designed by Professor W. F. M. 
Goss, is illustrated in Fig. 
127 by a line drawing. Being 
so simple in construction, it 
can readily be made in any 
factory or workshop with the 
materials available. It is 
essentially a differential lever 
measuring the difference in 
tension between the two sides 
of a belt. This lever is piv- 
oted at the point,' D, and to 
it are attached the shafts car- 
rying the pulleys A and B. 
Power transmitted is meas- 
ured by the product of the speed of the belt and the difference 
in its tension between the two sides of the dynamometer. 

The force tending to raise the left-hand end of the lever is 
assumed to be twice the tension ti, of the tight side of the belt, 
while that raising the right-hand side is twice the tension t 2 
in the slack side of the belt. These tensions on the two sides 
of the lever can be measured by weights Wi and w 2 suspended 
from its ends. The force tending to rotate the lever is therefore 




ffl 



^=^ 



Fig 127. — Goss Belt Dynamoneter. 



134 POWER PLANT TESTING 

twice the difference in tension on the two sides of the belt 
2(ti-t 2 ) and this force acts with a leverage AD=DB, when 
these two arms are made equal. If now the distance from the 
pivot D to the point of support of the weight Wi is made 
twice AD, and if the weight Wi is made equal to the difference 
in the tensions it will balance the lever. Or for these condi- 
tions we can write the equation, 

Wi=t 1 -t 2 . 

Now in any transmission system the difference in the tension 
of a belt or a rope on the two sides of a driven pulley multiplied 
by its speed is a measure of its power. If then, d is the diameter 
of the driven pulley C, plus the thickness of the belt or rope 
in feet, n is the number of revolutions of this pulley, and Wi is 
the weight in pounds on the left-hand side required to balance 
the lever ; when power is transmitted, then, 

Horse power transmitted = -. . . . (20) 

v 33,ooo v w 

To reduce the vibrations of the apparatus a dash-pot is 
connected to the right-hand side and also to prevent excessive 
movement of the lever when unbalanced, dash-pots are placed 
above and below the lever on the left-hand side. 

Differential Dynamometers. The apparatus illustrated in 
Fig. 128 is typical of a number of dynamometers indicating by 
means of a differential lever operated by gearing, the amount 
of power transmitted. 1 This is a very common form of trans- 
mission dynamometer. Power is received from the motor (or 
engine) by the shaft A, which is connected only indirectly by 
means of gears to the shaft A' opposite, which transmits the 
power to the work. To the adjoining ends of these shafts bevel 
wheels B and D are attached. The lever L turns on an axis 
concentric with the shafts A and A', in a plane perpendicular to 

1 Similar forms of differential dynamometers are known as White's, 
King's and Bachclder's. The first instrument of this kind, it is stated, 
was invented by Samuel White in 1780. These dynamometers are 
sometimes called epicyclic, signifying " wheels traveling around a circle 
or around another wheel." 



MEASUREMENT OF POWER— DYNAMOMETERS 



135 



them. It carries bevel wheels C and Ci, gearing with B and D, 
through which the power is transmitted. There is a tendency 
then for the left-hand end of L to go downward and for the right- 
hand end to rise. If, furthermore, the lever L were permitted to 
revolve, no work would be transmitted from B to D, and there- 



Weight 




Shaft to Work. 



Fig. 128. — Typical Differential Lever Dynamometer. 



fore D would remain stationary. As these gears are usually pro- 
portioned so that B revolves with twice as many revolutions 
in a given time as L, a weight placed on B at a given radius 
from the center will balance a weight twice as large at the same 
radius on the lever L. Then the moment of the force applied to 
the lever L to balance it must be twice as great as the moment 
of the force transmitted from C and Ci to D. If, therefore, 
1 is the length (feet) of the arm at which the weight w (pounds) 



136 POWER PLANT TESTING 

is applied, and n is the number of revolutions per minute of the 
shaft A, then the power transmitted per minute = 

— (foot-pounds), (30) 

and 

Horsepower (H.P.) = (31) 

33,ooo 

Now if the lever L is to be prevented from turning about 
its axis, a couple will be required which is twice the driving 
couple being transmitted. If, then, a weight of w pounds 
sliding on L as shown in the figure is placed at a distance 1 feet 
from the axis, so that the lever remains horizontal, the driving 
couple can be determined; and when the revolutions of the shaft 
A are known, the power can be found. A dash-pot D is 
usually attached to the differential lever L to reduce vibrations. 
This dash-pot should always be kept filled with glycerine or 
good clean oil. If the dash-pot is sticky consistent results 
cannot be expected. 

A Webber Differential Transmission Dynamometer as made 
commercially is illustrated in Fig. 129. The scale on the lever 
arm of this instrument is graduated into 100 divisions and a 
bell is provided which rings at every 100 revolutions. Since 
the horse power transmitted in one revolution per minute is 

irlnw . '. ' , , 
■- — equation (31), then the horse power corresponding to one 

division on the scale per 100 revolutions per minute is also 

33,ooo 

for a perfect calibration. 

It is interesting to observe that if we let 

v =the vertical force acting at C and Ci ; 

p = the vertical pressure between the teeth at each point of 

contact ; 
d = distance from the center of the rotation to C and Ci; 
l = the distance from the same center to the weight w. 

Then from the foregoing discussion it should be clear that 
2V=4p and wl = 2vd=4pd. Then if r is the effective pitch 
radius of the driving gear wheel B, ri is the radius of the small 



MEASUREMENT OF POWER— DYNAMOMETERS 



137 



bevel wheels, and the force producing the turning movement in 
the shaft A is represented by f, we have, 



and. 



fr=2pr!, 

f _2pr 1 _wlri 
r 2dr 



(32) 




Fig. 129. — Webber Differential Transmission Dynamometer. 



If we know the number of revolutions, then the space passed 
through by the force f can be calculated, and the work in foot- 
pounds is the product of the force times the distance passed 
through. The units given above are of course respectively in 
feet and pounds. 

Calibration of a Differential Dynamometer. 1. Examine 
the 1 dash-pot and observe whether the piston moves freely 
in the cylinder, particularly without " sticking." After the 
apparatus has been well oiled the position of the poise to make 



138 



POWER PLANT TESTING 



the lever arm horizontal should be observed for " no load." 
If this is not at zero then all the readings on the scale must be 
corrected by the amount of this zero reading. 

2. At each of the speeds required make a preliminary run 
without load and observe the reading of the poise when the lever 
is balanced. 

3. Attach a Prony brake to the shaft from which the power is 
to be transmitted and observe for a series of loads and speeds the 

readings of the poise 
on the dynamometer 
lever. 

4. For each speed 
plot a curve with theo- 
retical foot-pounds per 
minute by equation 
(30) as abscissas and 
actual foot-pounds 
per minute as deter- 
mined by the Prony 
brake as ordinates. 

Emerson Power 
Scales. Another very 
satisfactory instru- 
ment for the meas- 
uring of power trans- 
mitted by shafting is 
known as the Emer- 
son Power Scales. It 
is illustrated in Fig. 
130. 

It consists of a 
pulley C keyed to the shaft. To this pulley C a wheel B 
is connected loosely by studs EE projecting between and 
bearing against its spokes. The pressure exerted on these 
studs is proportional to the power transmitted by means of the 
pulley C, and this pressure is transmitted by a system of levers 
LL and bell-cranks MM to a sleeve A connected to a "weighing 
lever " W. The sleeve slides loosely on the main shaft. The 
amount of the pressure exerted on the studs is indicated for 
small values by a pointer P, moving over a graduated scale 




Fig. 130. — Emerson Power Scales. 



MEASUREMENT OF POWER— DYNAMOMETERS 



139 



F. For pressures beyond the limits of the graduated scale 
weights are placed on the scale pan N. A dash-pot D is pro- 
vided to prevent excessive vibrations and make the pointer 
" dead-beat." 

The scale F is calibrated to read the pressure (force) exerted 
by the torque of the pulleys C on the studs EE in pounds. The 




Fig. 131. — Flather's Hydraulic Transmission Dynamometer. 

work or " power " is calculated, therefore, by taking the product 
of this force times the distance moved through. If d is the 
diametral distance between the centers of the studs in feet, 
n the revolutions per minute and w the reading of the scales, 
then, 

rdnw 



Horse power 1 = 

33,ooo 

Compare with (31) for differential dynamometers, page 136. 



(33) 



140 



POWER PLANT TESTING 



A speed counter is attached to the apparatus for counting 
the number of revolutions. 

Flather's Hydraulic Transmission Dynamometers. A form 
of transmission dynamometer which is operated by hydraulic 




pCI 



X 



fe^ 



Fig. 132.— Diagram Showing Pulleys, Pistons, and Shaft of Flather's 
Dynamometer. 

pressure is shown in Fig. 131. The power shaft is keyed to the 
boss of a pulley B with two or more arms carrying hydraulic 
cylinders R. Projecting ends or studs from these cylinders bear 
upon the arms of a loose pulley A on the same shaft. The torque 




Fig. 133. — Details of Pistons and Cylinders in Flather's Dynamometer. 

imparted by the driving belt to the loose pulley A is thus trans- 
mitted to the shaft S through the liquid, and the resulting 
pressure is conveyed by radial pipes U to the hollow central 
shaft, and then to a pressure gage G. The hollow shaft is 
always filled with oil. In the figure an engine indicator I is 



MEASUREMENT OF POWER— DYNAMOMETERS 



141 



shown attached to the hollow shaft for recording the pressure. 
The loose pulley A drives the tight pulley B through its pistons 
which press on the oil in the cylinders carried by the tight 
pulley. By means of a worm drive the drum of the indicator 
receives its motion from the central shaft S. Figs. 132 and 
133 show more in detail the construction of the hydraulic 
cylinders on the pulley B. Fig. 134 shows typical indicator 



~^~4lfi0 



/^f\f JXrKfx ^j^\ 



Fig. 



[34. — Indicator Diagrams from Flather's Dynamometer Attached 
to a Mining Drill. 



diagrams from this apparatus. Both were taken from a dyna- 
mometer connected to a mining drill. The first was taken 
when the drill was sharp, the second when it was dull. 

Among the advantages claimed are: (1) its simplicity, (2) 
that it is not appreciably affected by the velocity of the shafting, 
(3) that no countershaft is required, (4) by connecting it to a 
recording gage a continuous diagram of the load can be obtained. 



CHAPTER VII 

FLOW OF FLUIDS 

The flow of fluids will be discussed under these heads: 
i . The flow of air. 

2. The flow of steam. 

3. The flow of water. 

The Flow of Air. When subjected to only a low pressure, 
air and many other gases are usually measured by a gas 
meter, of which there are many types sold commercially. There 
are, however, two general types: (1) wet and (2) dry. The 
former is by far the more reliable and should be always used 
in preference to a dry meter when it can be obtained. Wet 
meters receive their name from the water seal maintained in 
them. This seal must be always kept at a constant level, 
determined by calibration, 1 and before using such a meter in 
a test one should always observe whether the water level is at 
the standard mark. If it is not, then water must be added or 
withdrawn as the case may be. A section of a wet meter is 
shown in Fig. 135. It consists, as usually made, of a series of 
chambers arranged like an Archimedean screw, which are alter- 
nately filled and emptied. When air or any gas flows 2 into 
one of the chambers of the meter it accumulates over the sur- 
face of the water and by its pressure raises the chamber until 
it is filled. In the figure the gas enters at the dry-well, V, 
passes through the drum and out at the front end, then over 
the drum between it and the case to the outlet. In this way 
the drum is made to revolve to the left by the pressure on the 

1 Gas meters may be calibrated by any apparatus suitable for the 
displacement of gas as it is withdrawn by water. 1 1 is very necessary, 
of course, that when the weighings are made the pressure and temperature 
of the gas be accurately determined. 

2 The nature of specific gravity of the gas is not important, as gas 
meters are calibrated to record volumes, usually cubic feet. 

142 



FLOW OF FLUIDS 



143 



surface of the water below and the slanted partition C above 
forming an ever-increasing pyramidal space between the surface 
of the water and the plane of the slanted partition. Wet 




Fig. 135.— Typical Wet Gas Meter. 



meters are usually very accurate, while dry meters are not 
" supposed to be instruments of great accuracy." 

Pitot Tube for Measurement of Air. Probably the most 
accurate method of 
measuring air in large 
volumes is by means 
of a Pitot tube. A 
standard instrument of 
this kind designed for 
the measurement of air 
by the American Blower 
Company is shown in 
Fig. 136. 

It consists simply of two tubes, a small one, being placed 
inside of a larger one as illustrated in detail in Fig. 137. These 
tubes are arranged so that*each has a separate connection, 




Fig. 



■36. — "American Blower Co. 
Standard Pitot Tube. 



144 



POWER PLANT TESTING 



as at A' and B'. The lower end of the small tube is open at A, 
while the outside and larger tube has two openings at the 
opposite sides of B marked in Fig. 137, 2^ inches from the 
end at A. When the instrument is used it is placed so that the 

opening at A points 
against the direction 
of flow and receives 
the full effect of the 
pressure due to the 
velocity of flow. The 
side openings in B 
are subjected to only 
the static pressure. 
For convenience let 
p = velocity pressure 
and s = static pressure. For example, the difference in the 
levels in the manometer, a, Fig. 138, is therefore that due to 
(p + s)— s, or simply p, the velocity pressure . 

Pitot tubes are usually connected to manometers or prefer- 
ably to sensitive draft gages, showing the pressure in small 
fractions of an inch of water. When the end of the Pitot tube 




2 Holes at Front and Back of each .03 Diameter 
in Outer Tube 

Fig. 137. — Section of Standard Pitot Tube. 



For Pressures Above Atmospheric 




For Pressures Less Than 
Atmospheric 



Fig. 138. — Arrangement of Connections for Pitot Tube Measurements. 



at A' is connected to the left-hand end of a draft gage like 
those in the figures on page 24 and the end at B' is attached 
to the right-hand end, the instrument acts as a differential gage 
and the difference between the reading when thus connected 
and its zero reading is the pressure in inches of water corre- 
sponding to the velocity alone; that is, (p + s)— s. If we call 
this velocity pressure P when reduced to feet of water, and if h 
is the height or " head " also in feet of an equivalent column 



FLOW OF FLUIDS 



145 



of air producing the same pressure, then the velocity of the 
air v in feet per second is 

where g is the force of gravity (32.2), and 

wt. of a cu. ft. of water 



h = Px 



wt. of a cu. ft. of air 
62.3 » P 



wt. cu. ft. air 
v=6 3 .3^ : 



wt. cu. ft. air 



(34) 



In the following table the weight is given of dry air and 
also the weight of the dry air in, a cubic foot of air completely 
saturated with moisture (100 per cent humidity). The data 
given are at atmospheric pressure (14.7 pounds per square inch). 
By interpolating between these tables, the weight of air for any 
temperature and degree of saturation is easily obtained. 
Remembering also that the weight per cubic foot is directly pro- 
portional to the absolute pressure, the weight for any pressure 
is readily determined. Tables for determining the percentage 
of saturation by means of wet- and dry -bulb thermometers are 
given on page 331. 



Temper- 


Weight of 1 Cu. Wei 


jht of Dry 


Temper- 


Weight of 1 Cu. 


Weight of Dry 


ature, 


Ft. of Air 


in 100 % 


ature, 


Ft. of 


Air in 100 % 


Deg. Fahr. 


Dry Air. Lbs. Sat 


arated Air 


Deg. Fahr. 


Dry Air, Lbs. 


Saturated Air 


O 


•08635 


08623 


75 


.07424 


.07194 


10 


.08451 


08430 


80 




07355 


.07090 


20 


.08275 


08243 


85 




07288 


.06977 


3 2 


.08075 


08024 


90 




07222 


.06861 


40 


•07944 


07874 


95 




07157 


.06773 


45 


•07865 


07780 


100 




07093 


. 066 1 3 


5° 


.07788 


07688 


110 




06968 


06310 


55 


.07712 


07592 


120 




06848 


.00025 


60 


.07638 


07496 


150 




06511 


.04790 


65 


.07566 


07396 


200 




06018 


.01200 


70 


.07494 


07298 









1 The weight of 
(about 70 Fahr.). 



cubic foot of water at about "room " temperature 



146 



POWER PLANT TESTING 



Flow of Air through an Orifice. Air under comparatively 
high pressures is usually measured in practice by means of pres- 
sure and temperature observations made on the two sides of an 

orifice. Fig. 139 illus- 
trates the method 
with two pressure 
gages on opposite 

. sides of the orifice 

> and a thermometer 

I for obtaining the tem- 

139. — Measuring Flow of Air through an perature ti, at In 



1 r 



Fig. 



Orifice. initial or higher pres- 

sure, pi. The flow 
of air w, in pounds per second may then be calculated by 
Fliegner's formulas. 1 



:w = .53o. 






when pi is greater than 2p< 



(35) 



w = i.o6oXa 



/ P«(Pi- 



Pa) 



when pi is less than 2p a j . (36) 



where a is the area of the orifice in square inches, Ti is the 
absolute initial temperature in degrees Fahrenheit at the absolute 
pressure pi in the " reservoir," and p a is the absolute atmos- 
pheric pressure, both in pounds per square inch. 

For small pressures it is often desirable to substitute manom- 
eters for pressure gages. 

Flow of Air Measured by Cooling. This method depends 
on taking from the air an amount of heat 2 which can be meas- 
ured and then computing from the heat units absorbed and the 
difference in temperature and specific heat of the air, its weight 
and volume. The arrangement of the apparatus is shown in 
Fig. 140. A coil of pipes C of which the cooling surface is as 
equally as possible distributed over the section of the duct D, D' 

1 See Peabody's Thermodynamic:;, page 135, and Spangler's Applied 
'Thermodynamics, pages 12-13. 

2 The method will be equally applicable if heat is added, as for example 
by passing steam through the coil. This method is often used to cali- 
brate Pitot tubes and anemometers. 



FLOW OF FLUIDS ' 



147 



carrying the air to be measured, is used to absorb heat by. cir- 
culating water through it. Thermometers are arranged so that 
the temperatures of the air and of the water can be observed, 
and a platform scales is shown for obtaining the weight of 
water. Using the symbols ti and t 2 for the - initial and 
final temperatures of the air in degrees Fahrenheit, t' and 
t" for the temperatures of the water entering and leaving 
in degrees Fahrenheit, w a = weight of air passing through D, 
D' in pounds per second, Wo = weight of water collected in 
pounds per second, and 0.2375 = specific heat of the air at con- 



r mm i 



t 



£ 



ft 



Fig. 140. — Measuring Flow of Air by Cooling. 

stant pressure and at temperatures not much above " atmos- 
pheric," 1 then the heat absorbed by the water per second is 
Wo (t" — t') B.T.U. and this equals the heat lost by the air, or 
0.2375 w a (ti-t 2 ),and 



w (t"-t') 4 .2iiw (t"-t') 



0.2375 (ti-t 2 ) 



(ti-t 2 ) 



(37) 



Anemometers. A very convenient and simple method for 
measuring directly the volume of the air, or any gases, is by 
using an instrument called an anemometer. This instrument, 
Fig. 141, consists in its essential parts of a wheel having fiat 



1 The weight of a cubic foot of air is .0765 pound at 62 (522 abs.) 
degrees Fahrenheit and 14.7 pounds per square inch pressure. Since 
the volume is directly proportional to the absolute temperature, the 
weight at any other temperature is easily computed. 



148 



POWER PLANT TESTING 



or hemispherical vanes mounted on slender arms. The wheel 
must be made very light in weight, must be accurately balanced, 

and should move easily in 
its bearings. By its own 
motion it operates a re- 
cording mechanism indi- 
cating velocities in feet 
per minute (in English 
units) . 

The Flow of Steam. The 
flow of the steam from an 
orifice or nozzle has a very 
definite critical value when 
the final pressure is greater 
than 0.58 of the initial 
pressure. When the final 
pressure is less than this 
critical value the flow is 
expressed very accurately 
by the following empirical 
formula, based on the 
experiments of Messrs. 
Emswiler and Fessenden, 
in the Mechanical Labora- 
Michigan. Using the following 




Fig. 



41. — A Typical Anemometer for 
Measuring Velocity of Air. 

Of 



tories of the University 

symbols: 

pi= initial absolute pressure of the steam in pounds per square 

inch; 
-p 2 = final absolute pressure of steam pounds per square inch; 
a =area of the smallest section of the nozzle or orifice in square 

inches. 
Then the weight of the dry saturated steam discharged in pounds 
per second is approximately, 1 



pr 97 a 

J-± when p 2 is less than 0.580!- 

60.5 *" 



(38) 



1 A somewhat simpler formula, known as Napier's formula, which is 
accurate enough for most calculations, is the following: 



w = - ! — when p 2 is less than 0.58?! 
70 



(39) 



FLOW OF FLUIDS 



149 



Now since in the theoretical formulas the weight discharged 
is inversely proportional to the square root of the specific 

volume v, or w is proportional to -W±-i the formula above 

corrected for initial quality x of the steam is, 



Pi" 



6o.5\/x 



when p 2 is less than 0.58 pi- 



(40) 



J fe 07 

SI 

3 B 

VJ J2 0.5 

s 

SI 0.3 



0.1 



1.0 09 0.8 0.7 0.6 0,5 0.4 

Ratio of Final Pressure to Initial (El ) 
Pi 

Fig. 142. — Rateau's. Curve for Flow of Steam giving Values of the 
Coefficient K. 

When the steam is superheated the specific volume is con- 
siderably increased, and for this condition the author has found 
that the following equation gives very satisfactory results, 1 



















































































































£1 














































^ 












































L * 


$ 














































A 












































( 


?/ 














































#/ 
















































V 












































-c 


3 












































j 














































/ 
















































/ 






























































































/ 














CURVES FOR DISCHARGE OF STEAM 

MAINLY WHEN FINAL PRESSURE IS 

REATER THAN b&i OF INITIAL PRESSU 






/ 














IE 


~ 


/ 
































































































































































P 1 (a \ 

W = 6o.5(i+.ooo65d)' {4I) 

when, as before, p2 is less than o-58pi and where d is the number 
of degrees (Fahrenheit) of superheat. 

When the final pressure p 2 is greater than 0.58P1, the formu- 
las must be modified to correspond to the reduced flow observed 
by inserting a coefficient K as a factor in the right-hand member 

1 For a more extended discussion of the flow of steam see The Steam 
Turbine, by the author, pages 52-57. 



150 



POWER PLANT TESTING 



of the equations. Values of this coefficient are most conven- 
iently obtained from the curve in Fig. 142, which was plotted 
from the experimental results obtained by Professor Rateau 
of Paris. 

The Flow of Water. When the quantity of water to be 
measured is not too large it is most accurately determined by 
weighing in tanks placed on scales, or by direct measurement 
of volume in calibrated tanks or barrels. Sometimes it is 
impracticable to weigh or measure the volume of the water 
directly, particularly when it must be measured under pressure. 
For measurements in pipes up to 2 to 3 in diameter a water 
meter is generally used. 

A great many types of water meters are sold commercially 
and not very many are accurate, so that it is absolutely necessary 
Dial when using a meter 

to measure water in 
a test to calibrate it 
at least before and 
after the test, under 
the same conditions 
of temperature, pres- 
sure, and rate of 
flow of the water. In 
many plants where 
meters are used con- 
stantly, suitable con- 
nections are made to 
the discharge from 
the meter, so that 
at any time the flow 
through it can be 
diverted into a tank 




Pulsating Diaphragm Water Meter. 



in which it can be measured by volume or weighed. 

One of the best types of water meters is illustrated in Fig. 
143. This belongs to the class operating with a " pulsating 
diaphragm." The inclined shaft S on this diaphragm traveling 
around in contact with the peg P on the plate B moves the 
counting mechanism through intermediate gears. This dia- 
phragm, in the Thomson-Lambert meter (Fig. 144) is made 
of hard rubber reinforced with a steel plate, making it 



FLOW OF FLUIDS 



151 



much more durable than those made without reinforcing. 
As the side chambers are alternately filled and emptied, the dia- 
phragm is moved up and down with a kind of " pulsating " 
motion. A central spindle on the diaphragm is connected to a 
set of gear wheels operating the recording mechanism. 




Fig. 144. — Thomson-Lambert Water Meter. 



Worthington Water Meter. The Worthington water meter 
(Fig. 145) is also used frequently. It belongs to the type oper- 
ating in a cylinder by a reciprocating piston which is driven- back- 
ward and forward by the pressure of the water. Friction is an 
important element in meters of this type; but it is not injured 
by moderately hot water. 

The readings of a water meter are usually in cubic feet. 



152 



POWER PLANT TESTING 



A water meter is essentially a water motor adapted for operating 
the gearing connected to the counting mechanism. 

Frequent calibrations of water meters are necessary because 
they are likely to become more or less clogged with dirt and 
refuse. The readings are also affected by the temperature, 
head, and quantity of water flowing, as well as by the amount 
of air carried in the water. A meter should always be calibrated 
at least at two or three rates of flow, as it scarcely ever happens 
that the conditions of the test are so uniform that the meter 
will be used only for a certain predetermined rate of flow. 1 




Fig. 145. — Sections of a .Worthington Water Meter. 

Willcox Water Weigher. Automatic weighing or measuring 
devices are often used for determining the weight of condensed 
steam in engine tests or the weight of feed water in boiler 
trials. The Willcox weigher is a most satisfactory apparatus 
of this kind. It consists of a tank (Fig. 146) divided by a 
partition P into two compartments A and B, one above the 
other. The upper compartment A receives the inflow of water 
and the lower one B serves for measuring. Projecting into 
the lower compartment is a U-shaped discharge pipe C, which 
is always water-sealed. The upper end of the discharge pipe 
is covered by a bell float F, which is permitted a short up-and- 
down movement. In the upper compartment there is a short 
standpipe S, which is simply a hollow cylinder open at the top 

1 Calibration curves are usually plotted with meter readings as 
abscissas and actual volumes as ordinates. A curve should be plotted 
for each of the several rates of flow if they are different. Curves of 
meter readings (abscissas) and correction factors (ordinates) are also 
useful. 



FLOW OF FLUIDS 



153 



Gage Glass 



and bottom. The bell float F and the standpipe S are con- 
nected rigidly by a vertical rod (Fig. 147) so that they move 
together as one piece, and this is the only moving part in the 
apparatus. The lower end of this standpipe has a corrugated 
face, and when it is down in its lowest position its corrugated 
face rests on a soft seat or ring surrounding a circular opening in 
the partition P. This seat is made of a rubber composition 
which is not in- 
jured by boiling ^ ss * sCSSSSs ** s =^ {Vent 
water. The weigh- 
er can be used, 
therefore, with 
either hot or cold 
water without risk. 
In the opera- 
tion of the appa- 
ratus, when the 
standpipe S is down 
on its seat, water 
entering through 
the side inlet accu- 
mulates in the up- 
per compartment 
A until it overflows 
the top of the 
standpipe. The 
water then flows 
down through the 

hollow standpipe into the lower compartment until there is a 
sufficient amount to seal the lower edge of the bell float F. 
Then as more water accumulates the bell float rises, lifting the 
standpipe S from its seat and the water in the upper com- 
partment flows down into the lower one until the volume is 
that of a " unit charge " for the apparatus, when the " tripping " 
device discharges the water through the discharge pipe C. The 
" tripping " is accomplished by a " trip " pipe T, which is 
normally water-sealed, but which becomes unsealed when a 
"unit charge" has accumulated. While the water is accu- 
mulating in the lower compartment B the water in the left-hand 
leg of the " trip " pipe T is being slowly pushed down because 




Fig. 146. — Willcox Water Weigher (by Volume). 



154 



POWER PLANT TESTING 



Stand 
Pipe 



of the increasing pressure of the air under the bell float F, due 
to the increase of head of water, and a corresponding amount 
of water spills over the upper end of the right-hand leg R of the 
" trip " pipe into the discharge pipe C. Due to this action the 
water level in T is lowered until it reaches the bend in the lower 
end of the " trip " pipe. Under these conditions the water 
column in R exactly balances the head of water in the lower 
compartment B and the air entrapped in the float valve F 
has a function similar to that of a scale beam, balancing on one 
side the head of water in the tank and on the other side the head 
of the standard water column in R, 
which of course is always constant. 
At the instant this balance is secured 
a very small amount of water added 
in the lower compartment and the 
corresponding additional spill from R 
will destroy this equilibrium. Then 
the air compressed in the bell float F 
and the upper part of the discharge 
pipe breaks the water seal in R by 
suddenly discharging all the water 
in it. When the air pressure in the 
bell float F is thus reduced it drops 
down, carrying down with it the 
standpipe S in the upper compart- 
ment A. In this last operation the 
air is removed from the interior of the bell float F, and water 
flowing in to replace it will spill over the top of the discharge 
pipe C and will flow out at the other end till the lower cham- 
ber is emptied of the " unit charge." At this time, the 
standpipe S becomes seated, due to the pressure of the water 
above the bell float and to the downward suction of the syphon. 
Thus the standpipe is held tightly upon its seat only at the 
instant when tightness is required; that is, while the "unit 
charge " is being discharged. After the standpipe has seated 
water again accumulates in the upper compartment A and the 
cycle of operations is repeated. 

A mechanical counter shown at the side of the apparatus 
is connected to a ball float inside the lower compartment and 
registers the number of times the apparatus is tripped. An 




FLOW OF FLUIDS 



155 



rutomatic weigher of this kind is easily calibrated by weighing 
several " unit charges," and it can then be used with as great 
a degree of accuracy as can be expected with rapid weighings in 
tanks on platform scales. The Willcox weigher may be expected 
to weigh hot or cold water with a maximum error of not 
more than one per cent. 

Venturi Meter. An arrangement of piping in which there 
is a gradual narrowing of the section to a minimum and then 
a more gradual enlargement was invented by Mr, Clemens 
Herschel for measuring the flow of water. This apparatus is 
called a venturi meter and is shown in Fig. 148. Piesometer 
tubes (manometers) are arranged to indicate the pressure at the 
sections shown. Pressures at these sections will be denoted 
respectively by p m and p ra . 




Fig. 148. — Herschel's Venturi Meter. 

From Bernouilli's theorem 1 it follows that the relation between 
the pressure in pounds per square foot and the velocities in feet 
per second at the two section's v m and v n of a stream flowing 
through such a closed horizontal channel is given by 



2g £ + 2g' 



(42) 



where d is the density of the water in pounds per cubic foot. 
The volume of water flowing through any section is in cubic 
feet per second, if a represents the area of a section in square 
feet, 



a w ,v TO =a„v B =a, 



2g(Vm-Vn) 



(43) 



1 See Jamieson's Applied Mechanics, Vol. II., page 458. 



156 



POWER PLANT TESTING 



With suitable manometers or with gages the pressures p m and 
p n can be obtained, and since all other quantities can be repre- 
sented by a constant, k, we have 

Volume per Unit of Time =k(p OT -p n ). . . (44) 

The exceptional accuracy of this instrument for measuring 
the flow of water is well illustrated by the curve in Fig. 149, 



— : :::: — ::: — ::::— IT 


14 - > 


t 




13 : t 




19 T 


/ 




11 2 


_r 


in t 


10 /- 




-9 _1 


% J 


fe « / 


a -f 


7 




<D 7 


W r- 1 




j 


5 ^ 




. / 


S 


y 


3 Z_ 


+ ' 


^%- 


* 




1 ^-^ 




-«- — r" 



14 
13 

12 
11 
10 
9 

8 fe 
a 

7 S 
a> 

6 W 

5 
4 



15 20 25 30 35 

Discharge in Cubic Feet per Second 



Fig. 



[49. — Typical Curve Showing Extreme Accuracy of Venturi Meter. 



showing the flow as calculated from careful measurements of 
the head, while the barely perceptible dots shown on the curve 
indicate the results of actual observations by Pullen with a 
venturi meter. 

Flow of Water through Orifices and Nozzles. Theoretically 
the velocity of flowing water under any pressure is the same as 
the velocity attained by a body falling freely through a dis- 
tance equal to that head (h) as in Fig. 150. Furthermore this 
statement would be the same even if the water had no free 
surface, provided, however, the pressure at the orifice was that 
due to a head h. If then there is no loss of head due to friction 



FLOW OF FLUIDS 



157 



and eddies formed by the water passing through the orifice, the 
velocity of discharge, v, in feet per second is, 



v=\/2gh, 



(45) 



where g 1 is the acceleration due to gravity and h is the head 
in feet. 

If a is the area of the cross-section of the orifice in square 
feet, q is the quantity or volume of water discharged in cubic 




Fig. i 50. — Discharge of Water from an Orifice. 

feet per second, and assuming the stream is of the same cross- 
sectional area as the orifice, then, 

q=a\/2gh (46) 

Since the actual flow is less than the theoretical in most cases, 
and considerably less when the discharge is from a hole with 
sharp edges in a thin plate, a more general form may be written 
by inserting a suitable coefficient 2 of discharge, k, then, 

q=kav / 2gh (47) 

1 The value of g is approximately 32.2, so that equation (45) can be 
simplified into v = 8.02V / h. 

2 This coefficient is often called the coefficient of contraction. 



158 



POWER PLANT TESTING 



Calibration of Orifices and Nozzles. Water under a con- 
stant pressure is often measured by observations of the flow 
through either orifices or short nozzles which have been care- 
fully calibrated. The apparatus required consists usually of 
a suitably arranged standpipe to which the orifice or nozzle 
can be attached so that a given head of water can be main- 
tained 1 and a tank on scales (or calibrated for volumes) to 
receive the water discharged. 

A pressure of one pound per square inch is equivalent to a 
head of water at 62 degrees Fahrenheit of 27.72 inches, or 2.31 
feet. A normal atmospheric pressure (14.7 pounds per square 
inch) is therefore equivalent to a head of 33.96 feet of water. 
Then for a given pressure or head the quantity of water dis- 
charged in a given time is readily obtained and the coefficient of 
discharge can be computed by substituting the values of quantity 
of discharge q, the head h, and the area a, in formula (47) . 

Data and results should be tabulated in the form given 
below. The relative roughness of the edge of the orifice or of 
the inside surface of the nozzle should be recorded. 



FLOW OF WATER 



Form 

Flow of water through a . 

Date 

Form of orifice or nozzle . 
(Sketch) 



Observers 

Formula Diameter, feet 

.... Area, square feet . 



No. 

of 

Reading. 


Head 

in 
Feet. 


Time 
Seconds. 


Total 
Pounds 

Cu. feet. 


Pounds 

per 
Second. 


Cu. feet 

per 
Second. 


Coefficient 

of 
Discharge 

(k) 


Remarks. 


















Average 

















1 In many places a suitable pressure tank is not available, and in 
such cases the calibration can be made by attaching the orifices or nozzles 
to pipes carrying water under pressure. The readings of the pressure 
gage can be reduced to the equivalent head in feet, to which must be 
added, if the centre of the gage is higher than the orifice or nozzle, the 
distance in feet from the center of the nozzle to the center of the gage. 



FLOW OF FLUIDS 



159 




Curves. Curves should be plotted for each orifice or nozzle 
with head for abscissas and (i) the discharge (cubic feet per 
second) and (2) the coefficient of discharge for ordinates. 

Flow of Water over Weirs. When large quantities of water 
are to be measured, then orifices are unsuitable and it is customary 
to pass the whole body of water over a weir or gage notch. 
This consists of a board placed across the stream so that all the 
water must pass over it. The length of the 
notch is usually made less than the width of 
the stream to give definite conditions. This is 
accomplished most easily by sawing the notch 
out of a long board and beveling the edges. 

A typical arrangement for measuring the 
head of water on a weir is illustrated in Fig. 
151. The head must be determined with great 
accuracy, and this is done usually by means 
of a hook-gage, Fig. 152, and a suitable level. 



Fig. 



-A Weir for Measuring Water. 



Fig. 152. — A Hook 
Gage. 



The hook-gage consists of a sharp-pointed hook H, attached 
to a vernier scale V, intended to measure very accurately the 
amount the hook is moved. Before taking an observation the 
hook must first be submerged and then raised slowly till the 
point just breaks the surface of the water. The correct height 
of the surface is obtained at the instant when the point of the 
hook pierces it. - The head h of the water flowing over the 
weir (Fig. 151) is obtained by setting by means of a straight-edge 



160 



POWER PLANT TESTING 



SE and the level L the point of the hook at the same level 
as the crest of the weir. The height observed in this posi- 
tion is called the zero head. It is to be subtracted from all 
other readings to get the head of water flowing. The hook- 
gage must be placed in such a position on the upstream side 
of the weir where the surface has no appreciable velocity and 
where there is very little disturbance due to eddies. In terms of 
the following symbols, 

q = quantity or volume of water discharged in cubic feet per 

second ; 
h-=the head in feet on weir measured in still water; 
b= breadth of the weir in feet; 
n=the number of contractions; 
k = coefficient of discharge. 



q =2 /3kh 3 / 2 (b — o.inhK^g. 



(48) 




Weir with a Triangular Notch. 



This is the well-known Francis formula for a rectangular notch. 
The ordinary rectangular notch has two contractions, one at 
each end. Triangular notches in weirs are sometimes used. 
One of these in the form of a right-angled isosceles triangle is 
shown in Fig. 153. It has the advantage of giving the same 
form of stream whatever the size of the notch or the height of 



FLOW OF FLUIDS 



161 



water passing through. It is, therefore, particularly suitable for 
measuring a flow of water which is somewhat variable. The 
quantity of water discharged over a triangular weir or notch is, 



q=4/i5kbh 3/2 \/2g. 



(49) 



(50) 




When the angle is 90 °, 

b=2h and q =4.26 kh 5/2 . 
Also when the angle is 6o°, 

b=2htan30° and q=2.47kh 5 ^ 2 . . . . (51) 

Any mistake made in determining h will produce a larger 
percentage error in the results 
with the rectangular and tri- 
angular notches than with an 
or'fice. Where great accuracy 
is desired and the quantity of 
water to be handled is not too 
large, an orifice calibrated and 
used in the bottom of the tank 
as shown in Fig. 154 is to be 
preferred to measurements with 
a weir. This remark is par- 
ticularly applicable in connec- 
tion with the measurements of 
cooling (circulating) water in 
tests of large steam engines and 
turbines. 

Use the same form for data as 
given for Calibration of Orifices 
or Nozzles on page 158. 

Curves should be plotted with heads for abscissas and (1) 
the discharge (cubic feet per second) and (2) the coefficient 
of discharge for ordinates. 



: 7-:\V'////4;— 



Fig. 



54. — Best Kind of Orifice 
for Engine Tests. 



CHAPTER VIII 
CALORIFIC VALUE OF FUELS— SOLID, LIQUID, AND GAS 

Calorific Power is a term applied to the quantity of heat 
generated by the complete combustion of a definite quantity 
of fuel. In order to insure rapid and complete combustion the 
fuel is preferably burned in an atmosphere of oxygen under pres- 
sure. This calorific power of fuels is expressed in the English 
system as British thermal units per pound, and in the metric 
system as calories per kilogram. 

The quantity of heat generated by combustion is measured 
by the rise in temperature of a given weight of water in a 
calorimeter, of which the cooling effect or water equivalent k 
has been determined, and the temperature of the gas escaping 
has been reduced to that of the room. Now if, 

W/ = weight of the fuel in pounds, 

w,„ = weight of the water in pounds, 

k = water equivalent x of the calorimeter, in pounds, 

ti = initial temperature of water, degrees Fahrenheit, 

t 2 = final temperature of the water, degrees Fahrenheit, 

Q =heat generated, B.T.U., 

1 Water equivalent is used to express the heat-absorbing effect of 
the calorimeter as equivalent to that of a weight of water. This may 
be found as for calorimeters used for determining the quality of steam 
by the hot- water method (see page 64), by taking the sum of the prod- 
ucts of the weights and specific heats of the various parts of the calori- 
meter (see Calorific Power of Fuels, by H. Poole, pages 14 and 15), or by 
comparing the results obtained with those that should have been secured, 
if there had been no absorption of heat, by the combustion of some fuel 
of which the heat value is known; as, for example pure carbon in oxygen 
gas. 

Corrections for radiation can be practically eliminated by having the 
temperature of the water in the calorimeter before ingition as much below 
the " room " temperature as the final temperature is above. 

162 



CALORIFIC VALUE OF FUELS 



163 



then the calorific value H per pound of fuel in British Thermal 
Units is, 

Q ( Wu ,+k)(t 2 -t,) 



H 



W/ 



w/ 



(52) 



Bomb Calorimeters. Formerly the calorimeters used for 
burning fuels in an atmosphere of oxygen were arranged for 
combustion at constant pressure, but since it was found that 
more reliable results could be obtained generally with apparatus 
maintaining a constant volume, the former type is not now much 
used. When the combustion takes place 
at constant volume, the vessel receiving 
the charge of fuel and oxygen must be 
designed to withstand a great pressure, and 
therefore on account of the massive con- 
struction required the vessel is called a 
bomb calorimeter. The essential part of 
such a calorimeter is the strong steel vessel 
or bomb similar to Fig. 155. It consists 
essentially of a steel shell S capable of 
resisting with safety a pressure of about 
750 pounds. This shell is usually provided 
with a coat of enamel or a lining of nickel 
on the inside and is nickel-plated on the 
outside . The coating or lining on the inside 
is intended to resist corrosion and oxidiz- 
ing action during the combustion. The 
advantage of the nickel lining over the 
coat of enamel is that when it is worn 
out or broken it can readily be replaced 

and at much less expense than the enamel. The shell is closed 
at the top by an iron cover or cap which is to be made tight 
by screwing down on a lead washer with considerable force, 
using a long wrench. At the top of this cover or cap there is a 
conical seated valve, which is screwed in through the gland 
and stuffing-box G, by attaching a wrench at P. The valve 
and its seat are made of good nickel, as this metal is not easily 
oxidized. A wire electrode, which is well insulated from the 
cover, extends into the shell and conducts the electric current 
for firing the charge of fuel, which is placed on a platinum dish 




Fig. 155. — Section of 
a Bomb Calorim- 
eter. 



164 



POWER PLANT TESTING 



or crucible supported by another wire attached to the cover on 
the inside. 

Usually one gram of fuel is put into the dish to make a test 
for calorific value. A small iron wire (which was previously 
weighed) is then suspended over the dish between the electrode 
and the wire support for the dish. The cover should then be 
screwed on with a long wrench, the shell itself being held in a 
vise. The complete Mahler apparatus is shown in Fig. 156, 
showing the cylinder of oxygen 0, the pressure gage M, the 
calorimeter vessel D. The end of the conical-seated valve 
(Fig. 155) is attached by means of pipe connections, preferably 



Union for Attachment 
of Bomb when Filling 
with Oxygen. 




Fig. 156. — Complete Mahler Apparatus. 



flexible, to the union U and to the valve W, which because of the 
high pressure should be opened slowly and carefully, and allow 
sufficient oxygen to pass into the bomb to provide a consider- 
able excess above that actually required. The pipes for con- 
necting the bomb to the oxygen cylinder should connect also 
with a pressure gage as shown, so that the pressure in the bomb 
can be regulated. For the combustion of coal a sufficient 
volume of oxygen is admitted to Mahler bombs of the usual 
size to make the pressure in the bomb from 200 to 300 pounds 
per square inch. Now close the valve on the oxygen cylinder 
and the conical seated valve on the bomb, removing also 
the connections between the bomb and the oxygen cylinder. 



CALORIFIC VALUE OF FUELS 165 

The fuel, especially if it is coal, should not be too fine, because 
if accidentally the oxygen should be allowed to go in a little 
too rapidly, some of sample of the coal will be blown out of the 
dish and will probably not be burned. The bomb should then 
be placed in the calorimeter vessel D, which should then be 
filled with a quantity of water previously weighed to fill it 
to about the level indicated in the figure. Place the calo- 
rimeter thermometer T into the vessel, being careful that the 
end will not be touched and broken by the stirrer or other 
parts, and then after agitating the water for a few minutes to 
establish a uniform temperature, the observations can begin. 
The temperature should be very carefully observed for five 
minutes and recorded minute by minute, to determine the 
rate of variation of temperature before combustion. Then the 
electric circuit should be made and the combustion will, of 
course, begin immediately; but some little time will be re- 
quired for the transmission of the heat generated to this water. 
Now take the temperature at the end of a minute after making 
the electric circuit; and continue observing the temperature 
every minute till it reaches its maximum value and begins to 
fall off regularly. Continue the observations for five minutes 
more to determine the rate of the fall of the temperature. The 
stirrer should be worked continuously but not too rapidly 
throughout the test, being careful, however, that the thermom- 
eter is not broken. When the observations have been finished, 
the conical-seated valve should be opened first to relieve the 
pressure and then the cover or cap can be unscrewed and 
removed. 1 

The method described for the use of the Mahler bomb calo- 
rimeter can be applied also for determinations of calorific value 
of liquid fuels. Heavy oils can be weighed directly in the 
platinum dish or crucible, but light oils which are easily vapor- 
ized must be put into specially prepared glass bulbs which are 
broken to allow access of the oxygen, just before the cover is 

1 Some engineers wash out the inside of the bomb with a little dis- 
tilled water to collect the nitric and sulphuric acids formed. Usually, 
however, this correction for acids is not made, as the heat liberated in 
the formation of the acids is usually less than one-third of one per cent, 
which, of course, would be subtracted from the calorific value obtained. 
If the reader is interested he will find the method explained with the 
necessary data in the Calorific Power of Fuels, by H. Poole, page 62. 



166 POWER PLANT TESTING 

put on the bomb. If sufficient oxgyen is provided in every 
case there will be complete combustion in the calorimeter with 
no other refuse than the cinders remaining. 

A specimen calculation is given below : 

Weights, — coal, .0030 lb.; 1 water in calorimeter, 4.85 lbs.; 
water equivalent of bomb, etc., 1.10 lbs. Weight of iron wire, 
.0002 lb. 

Preliminary Observations. 

Beginning 60.23 F., 3 minutes, 60. 2 6° F., 

1 minute, 60. 24 F., 4 minutes, 60. 27 F., 

2 minutes, 60. 25 F., 5 minutes, 60. 28 F. 

Rate of variation before combustion, a — — : : — =.oi° F. 

Observations during Combustion. 

6 minutes, 65. 45 F. 

7 minutes, 67.29° F., 

8 minutes, 67.38° F., max. 2 

Observations after Maximum was reached. 

9 minutes, 67.34° F., 12 minutes, 67.28° F., 

10 minutes, 67.32° F., 13 minutes, 67.27° F., 

11 minutes, 67.30° F. 

Rate of variation after maximum, a™=— — — = .022° F. 

5 

The rate of variation of temperature before combustion was 

for cooling the water and that after combustion was for a loss 

of temperature by the water. Evidently, then, the two rates 

are opposed in effect and the true average rate of variation is 

a„= : '- = +.006° F per minute. 

2 

1 The coal had been warmed at a temperature of about 240 to 280 
degrees Fahrenheit before weighing, in a crucible over a Bunsen burner 
or an alcohol lamp to drive off the moisture. 

2 Some engineers make a curve of temperatures (ordinates) and time 
(abscissas) and use for the final temperatures in the calculations the 
value from the curve, when the part of the curve representing the 
Gooling becomes a straight line. The difference in numerical values is 
usually very slight. 



CALORIFIC VALUE OF FUELS 



167 



Three minutes (5-6, 6-7, and 7-8) were required for com- 
plete combustion or for the water to reach the maximum tem- 
perature. Total cooling correction to be added to the observed 
rise in tempera- 
ture is therefore, 
3X.006-.018 F. 

The total rise as 
corrected is, 7.10 + 
.018 = 7.118° F. 

The quantity of 
heat generated is, 
therefore, Q = (4.85 
+ 1.10) X7-n8 = 
42.35 (B.T.U.) for 
.0030 lb. of coal; 
and from this result 
must be subtracted 
the heat of combus- 
tion of the iron wire 
.0002X3000 1 oro.6o 
B.T.U. The net 
value of the heat 
generated from the 
coal is, therefore, 
42.35 - .60 = 41.75 
B.T.U. 

A modification of 
the Mahler bomb 
calorimeter has been 
designed by Atwa- 
ter, 2 Fig. 157, and 
another by Emer- 
son, Fig. 158. The 
former consists of 
the shell of the 
bomb A, the cap 

C, screwed on numerous threads to the shell, and holding down 
the cover B. Into the vertical neck of this cover a screw E, 

1 The calorific value of pure iron is about 3000 B.T.U. per pound, 

2 Atwater, Bulletin No. 21, U. S. Dept. of Agriculture, 




|pWll^^^ 



Fig. 



157- 



-Atwater's Fuel Calorimeter. 



168 



POWER PLANT TESTING 



holding another screw F, is fitted and is to be turned down 
tightly, a lead washer serving as " packing." A small passage 
for the admission of oxygen from G is opened and closed as 
required by turning the screw F operating a needle-valve. 
A wire H of platinum or other non-oxidizable metal passes 
through the cover B and is insulated from it by a collar of 
hard rubber. Another wire rod I is attached to the lower 
side of the cover and electrical con- 
1 nection is made between the two 

wires H and I by a small iron wire 
stretched between them. A plati- 
num crucible provided for receiving 
the fuel is supported by a " screw " 
ring. Ball bearings of hard steel 
are sometimes placed between the 
cover and the cap to reduce friction 
when screwing down. Holes located 
in the sides of the cap are for the 
attachment of a long spanner wrench 
when turning down the cap. A 
hand-stirring device S is used for 
agitating the water in the vessel Q. 
The usual arrangement of the 
oxygen tank, pressure gage and 
tubing for charging an Atwater 
calorimeter is illustrated in Fig. 
159. A pellet press for com- 
pressing samples of fuel into a 
suitable size to burn in the cru- 
cible of this calorimeter is shown 
in Fig. 160. 
Fig. 158 shows another form of bomb calorimeter (Emer- 
son) of which the Mahler is typical. It consists of a nearly 
spherical shell S, divided into two parts which are screwed 
together by the ring R. Powdered fuel is placed in the crucible 
C and is ignited electrically by the current passing through the 
water in the vessel Q from the terminal at A, then through an 
insulated contact point P in the bottom of the calorimeter to a 
small platinum or iron wire in the crucible C, which becomes 
heated by the passage of the current to a white heat, igniting 




Fig. 158. — Emerson's Fuel 
Calorimeter. 



CALORIFIC VALUE OF FUELS 



169 




the fuel. One end of this small wire is fastened to make elec- 
trical contact with the lining of the calorimeter, which in turn 

is connected electrically with the 

plug and terminal at B. 

The outer vessel is to be 

filled with water to the top. The 

stirring device consists of small 

propellers F, on a vertical shaft 

operated by a small electric motor 

M. 

Parr Calorimeter. It is not 

always convenient to secure a 

supply of oxygen under pressure 

for use in a Mahler bomb, and con- 
sequently another type ! of fuel 

calorimeter, known as Parr's, has 

found considerable use, especially 

for relative determinations in power 

plants. The results obtained can 

never be depended on to be as 

nearly accurate as determinations 

with one of the bomb type. Fig. 

161 illustrates a simple form of Parr 

calorimeter. Sectional views of the two kinds of calorimeter 

vessels used are shown in Figs. 162 and 163. In the former the 

ignition is accomplished by dropping a hot wire through the 

neck into the shell A of 
3 the calorimeter. The 
cover is attached to the 
shell by means of a 
threaded nut F. A charge 
for the bomb consists of 
about .004 pound of pul- 
verized coal from which 
the moisture has been 
driven off by warming 
for about an hour at a 
temperature of about 240 

to 280 degrees Fahrenheit, and eighteen times as much by weight 

of sodium peroxide, which supplies the oxygen needed for com- 



Fig. 159. — Apparatus for 
Charging Atwater's Calorim- 
eter with Oxygen. 




Fig. 160. 



-A Pellet Press for Compressing 
Samples of Fuel. 



170 



POWER PLANT TESTING 



bustion. The charge should be well mixed by shaking the shell 
after the cover has been securely fastened. The cover must be 
attached very securely by turning up the nut with a long wrench, 
while the shell is held in a vise or in some similar manner, because 




Fig. 161. — Typical Parr Calo- 
rimeter. 



Fig. 162. — Parr 
Bomb for Hot 
Tube Ignition. 



Fig'. 163.— Parr 
Bomb for Elec- 
trical Ignition. 



there is a violent explosion when ignition takes place. When the 
hot wire is put into the tube in the long neck L, the cap R at 
the top must be struck quickly with a mallet before the wire 
cools in order to open the valve M, which opens inward into 
the shell and permits the wire to fall through. To be certain 
of obtaining a good result the wire should be heated almost 



CALORIFIC VALUE OF FUELS 



171 



to a white heat. The rise of the mercury in the thermometer 
will indicate when an explosion has occurred. 

The calorimeter is provided usually with wings or small 
propeller blades for agitating the water in the vessel O. The 
small pulley P (Fig. 161) shown at the top of the neck is used for 
turning the calorimeter bodily in the water when supported on 




Fig 



Parr Calorimeter with Motor Stirring Device. 



the pivot F, shown at the bottom of the figure. The water 
equivalent of the calorimeter is determined in the same way as 
for other fuel calorimeters. Fig. 164 shows the Parr calorimeter 
as designed for electrical ignition and with a stirring device 
operated by an electric motor. 

Allowance must be made in the calculations for the heat 
of combustion of the sodium peroxide, which for the propor- 
tions given is approximately 27 per cent of the heat generated. 



172 



POWER PLANT TESTING 



Carpenter's Calorimeter. There are few calorimeters in 
which the oxygen is supplied at constant pressure which are 
altogether successful. One of the best forms of an apparatus of 
this kind has been designed by Carpenter, especially for coal 
determinations. With this apparatus no thermometers are 
needed, as the rise in temperature is measured by the expansion 

of the mass of water sur- 
rounding the combustion 
chamber. 

This apparatus is 
shown in Fig. 165. It 
consists of a combustion 
chamber 15, provided 
with a removable bottom 
17, through which the 
tube 23, supplying the 
oxygen, passes into the 
combustion chamber. 
Electric current for igni- 
tion is conducted through 
the wires 26 and 27. The 
removable bottom sup- 
ports also the asbestos 
cups or crucibles 22, used 
for holding the sample of 
coal to be burned. Just 
beneath the crucibles a 
silver mirror 38 is pro- 
vided to deflect the heat. 
The plug containing the 
wires and the oxygen 
pipe 23 is made of 
alternate layers of as- 
Products .of combustion leave the 
spiral tube, the parts of 




Fig. 165. — Carpenter's Calorimeter. 



bestos and vulcanite. 

combustion chamber through 

which are marked 28, 29, 30, and 31, into the small vessel 

39, attached to the outer casing of the instrument, and are 

finally discharged into the air from a small hole 41, in the side 

of the vessel. The pressure in the chamber 39 is indicated by 

a manometer gage 40. The inner casing of the instrument 1, 



CALORIFIC VALUE OF FUELS 173 

containing the water for absorbing the heat generated, is nickel- 
plated and highly polished to reduce radiation as much as 
possible. An open glass water gage 10 passes through the 
casings and extends below the water level. This water gage, 
with the scale attached to it, replaces the thermometer used in 
other calorimeters for measuring the rise in temperature. The 
scale is graduated to read inches, and it is calibrated usually 
by burning coke in the calorimeter, and determining thus the 
rise of the water level for a determinable weight of pure carbon. 
A calibration curve is usually supplied with the instrument. 
By moving the diaphragm 12, by means of the screw 14, the 
water level can be regulated, as well as the " zero " level in 
the glass water gage 10. A funnel 37 is provided for filling 
the instrument, and by inverting it, this funnel can be used also 
for draining. The instrument holds 5 pounds of water, and 
2 grams of coal is the amount taken usually for a charge, 
requiring about twenty minutes for complete combustion; 
powdered coal is used. The asbestos cup should be heated in 
the flame of a Bunsen burner before it is weighed. The 
charge of dried coal should then be put into it and weighed 
again. The difference will be the weight of the coal used. 
Now put the charge into the combustion chamber 15, place 
the platinum ignition wire above the coal, connect wires 26 
and 27 to the battery, and as soon as the heat generated causes 
the level of the water to rise in the glass water gage 10, open 
the valve in the pipe discharging oxygen into tube 23, and then 
by pulling down the platinum wires to touch the contents of 
the crucible, the coal will be kindled. At the same time the 
reading of the glass scale opposite the gage glass 10 must be 
observed and recorded. Progress of the combustion can be 
observed through the glasses 33, 34, and 36, arranged vertically 
over each other for this purpose. As soon as the combustion 
is complete observe the time and the reading of the scale opposite 
the glass water gage 10. The difference between this last 
reading and the one taken at the beginning of the test is called 
the " actual " scale reading. 

The correction for radiation is made by observing the reading 
of the scale of the water gage after the oxygen has been shut 
off, a length of time equal to that required for the combustion. 
The difference between this reading and the " actual " reading 



174 



POWER PLANT TESTING 



is to be added to the " actual " reading to obtain the corrected 
reading. 

By weighing the asbeslos cup after the test is finished 
and subtracting from this weight that obtained previously for 
its weight empty, the weight of ash is determined. 

In order that Carpenter's calorimeter may give determi- 
nations of heat values that are at all accurate, all the air must 
be removed from the water used, as the presence of air x will 
affect the relative level of the water in the gage glass for a given 
rise in temperature. The oxygen must also be supplied at a 
constant pressure, maintaining the pressure indicated by the 
manometer gage at the value for which the calorimeter was 
calibrated. Most calibration curves are made for a pressure 
of about 10 inches of water. The apparatus can be made to 
give good comparative results when operated carefully and 
" according to directions." In general, the statement is often 
made that coal calorimeters intended for combustion at constant 
pressure will usually give nothing more than " faint approxi- 
mations " to correct results. The same can be said, however, 

of nearly all the calo- 
rimeters if they are 
not very carefully 
manipulated. 

When making cal- 
orific determinations 
of coal the distinction 
must be carefully 
made between results 
obtained per unit 
weight of combustible 
or per unit weight of 
coal (including mois- 
ture and ash). 

Junkers Calorim- 
eter for Liquids and 
Gases. An apparatus 
for determining the 
calorific power of gases is shown in Fig. 166 and Fig. 167. 

1 About 2 inches of kerosene oil is usually put into the glass water 
gage to prevent air from coming into contact with the water. 




Jig. 166. — Junkers Calorimeter with Auxil 
iary Apparatus. 



CALORIFIC VALUE OF FUELS 



175 



The gas flowing in pipes at the left (Fig. 166) passes through 
the meter A, then through the regulator B, and is burned in a 
type of Bunsen burner C, in the lower part of the calo- 
rimeter. This instrument consists of a cylindrical copper 
vessel through which water is constantly circulating. The 
gases from the Bunsen flame in the calorimeter pass up 
through the hollow central portion 
of the instrument and near the top 
are deflected downward through a 
group of small tubes arranged in 
an annular ring between the outside 
and inside walls of the calorimeter. 
Around these tubes water is kept 
circulating continuously to absorb 
the heat generated by burning the 
gas tested. After leaving these tubes 
the products of combustion dis- 
charge first into a chamber 31 (Fig. 
167) and then into the air through 
the flue D. In order to keep the 
flow of water as regular as possible 
it is brought from the supply pipe 
G into a small reservoir in which 
the water is kept at a constant 
level (constant head) by means of 
an overflow pipe H. The water 
supplied to the calorimeter passes 
down through the pipe 6, through a 
valve at I, and discharges at K, 
running into a vessel in which it 
is weighed. A graduated tube Q „ 
(Fig. 166), is provided to collect 
the moisture from the steam 

that is condensed. The condensed steam collects in the 
combustion chamber 31 and escapes through the tube 35. 
A thermometer N, in a cup near the valve I, indicates the 
temperature of the water entering the calorimeter, and one 
at M shows the temperature of the water leaving. The tem- 
perature of the products of combustion (burned gases) is 
indicated by the thermometer 0, in the gas flue. The calo- 




67. — Section of Junkers 
Calorimeter. 



176 POWER PLANT TESTING 

rimeter is provided with an air jacket and is covered with 
sheets of copper, nickel plated and highly polished so that 
the radiation loss is considered negligible. If, then, the flow 
of water and the rate of burning the gas are regulated so 
that the temperature of the products of combustion 1 as indi- 
cated by the thermometer at 0, is the same as the tempera- 
ture of the air surrounding the calorimeter, practically all 
the heat generated by the burning gas is absorbed by the 
water. The rise in temperature of the water is observed by 
reading the thermometers at N and M. 

Now if the temperatures of the water at the inlet and the 
discharge have been observed and the weight of the water flow- 
ing has been determined while, for example, a cubic foot of gas 2 
has been burned, then "the difference in temperature in degrees 
Fahrenheit times the weight of water in pounds gives the heat 
value in British thermal units per cubic foot of gas. 

For some calculations relating to the efficiency of heat 
engines it is desirable to know the number of heat units repre- 
senting the calorific value of the gas when the steam formed 
in the combustion is not condensed but is carried off with 
the products of combustion. To determine this value, some- 
times called the "low heat value" of the gas, the latent heat 
at atmospheric pressure of the amount of condensed steam 
collected must be subtracted from the value obtained by 
multiplying together the rise in temperature and the weight 
of water used. This correction is usually about two per cent. 
This apparatus, although it operates by a constant pressure 
method, gives very satisfactory determinations. 

Fig. 168 shows a balance and lamp attachments for a 
Junkers calorimeter set up for determining the heat value of 
liquid fuels like gasoline, kerosene, crude oil, etc. The heat 



1 Heat lost in products of combustion is explained in Stillman's 
" Engineering Chemistry," pages 161-165. See also in this book pages 
196 and 224—226. 

2 In order that results can be compared, it is customary to reduce 
the calorific power to terms of heat units per cubic foot of gas at a " stand- 
ard " temperature and pressure as for example, 32 degrees Fahrenheit 
and 14.7 pounds per square inch, assuming that the volume of the gas 
is proportional directly to the temperature and inversely to the pressure, 
or else by determining the specific volume of the gas to calculate the heat 
units per pound. 



CALORIFIC VALUE OF FUELS 



177 




Fig. i 68. — Balance and Lamp for 
Burning Oils in Junkers Calorim- 
eter. 



generated is measured in the same way as when gas is burned 
and the weight of oil used is determined by weighing on the 
balance to which the lamp L is attached. 

Calorific Values from Chemical Analysis. Dulong stated 
a long time ago that the heat generated by burning any fuel 
was equal to the sum of the 
" possible heats " generated 
by its component elements, 
less that portion of the 
hydrogen which combined 
with the oxygen in the fuel 
to form water. When hy- 
drogen and oxygen exist 
together in a compound in 
the proper proportions to form 
water, the combination of 
these elements has no effect 
on the calorific value of the 
compound . No w the calorific 
value of a pound of carbon is 

14,600 B.T.U. and of a pound of hydrogen is 62,000 B.T.U., so 
that by Dulong's formula, the calorific value of a pound of 
fuel would be stated, using these values, as 

x = 14,600c + 62,000 (H— — ) + 4,000 S, 

o 

here C, H, and S are respectively the weight of the carbon, 
hydrogen, oxygen and sulphur in a pound of fuel. As the result 
of testing the forty-four different kinds of coal with his bomb 
calorimeter Mahler. developed the following formula, using the 
same symbols used in Dulong's, 

x = 200.5 + 67511-5,400. 

Using this latter formula Lord and Haas 1 determined for a series 
of 40 Pennsylvania and Ohio coals which they had analyzed 
and computed the calorific values that the maximum differences 
between the calculated results and the determinations with 
a bomb calorimeter were from 2.0 to — 1.8 per cent. With 
fuels like coke, charcoal, and anthracite coal, in which the 



Trans. American Inst, of Mining Engineers, Feb., 1897. 



178 POWER PLANT TESTING 

content of volatile matter is small, the calorific values calcu- 
lated from an accurate analysis are usually in very close 
agreement with accurate calorimeter tests, but with coals 
having more than 20 per cent of volatile matter there is likely 
to be considerable error. 

Proximate Analysis of Coal. For all tests in which an 
analysis of the coal or its calorific value is to be determined, 
it is very necessary that the sample to be tested be selected 
with the greatest care. The method generally adopted for 
obtaining a fair sample is known as ' ' quartering, ' ' as explained 
in the Rules for Conducting Boiler Trials adopted by the 
American Society of Mechanical Engineers. (See page 210.) 
The utmost care must be taken that the amount of moisture 
in the sample received for analysis is the same as that in the 
original condition, or more specifically in a boiler test, at the 
time when the coal used in the test was weighed. For this 
reason samples of coal should be transported and stored in 
air-tight preserving jars or similar vessels. It is not unusual, 
moreover, to find that coal containing 10 per cent of moisture 
will lose as much as 2 or .3 per cent of its moisture in the 
process of careless sampling, crushing, resampling, etc., while 
if it is allowed to remain exposed to atmospheric conditions 
for a considerable time in a warm room as much more may be 
lost by evaporation. 

Moisture Determinations. Determinations of moisture are made 
by careful engineers as soon as permissible after the sample has 
been procured and with the coal in as large pieces as possible. 

A good method for making the moisture determinations 
for anthracite and semi -bituminous coals is to place a weighed 
sample on top of the hottest part of a boiler setting or a flue 
and weigh it again after drying for twelve hours. A good 
laboratory test for the same kinds of coal is to place a sample 
weighing about .05 pound in an air or sand bath for one 
hour at a temperature of from 220 to 230 degrees Fahrenheit, 
and weigh again when the sample is cool. 1 The difference in 
weight is the amount of moisture in the sample. 

1 While the sample is cooling there is the possibility that it may 
absorb moisture from the air unless it is placed in a desiccator till cool. 
It is difficult to get accurately the weight of hot bodies on account of 
the air currents produced. 



CALORIFIC VALUE OF FUELS 179 

When coals taken from the mines west of the Pittsburg dis- 
trict or other coals containing inherent moisture are to be tested 
for moisture, a different method must be adopted. The sample 
of coal is to be spread out in a thin layer and exposed for 
about four hours to the atmosphere of a warm room. The 
difference between the weighings before and after this exposure 
is the weight of surface moisture. Then crush all of this sample 
to produce coarse grains measuring not more than one-sixteenth 
inch on a side, mix it thoroughly, and select from it a quantity 
weighing from .05 to .125 pound, and dry it for one hour, 
in an air or sand bath in which the temperature is maintained 
at from 240 to 280 degrees Fahrenheit. Now weigh it again 
and then continue the heating between these limits, weighing 
every hour till two of these weighings are the same or the weight 
begins to increase due to oxidation of the coal. The difference 
between the original and the minimum weight of this sample is 
called the moisture in air-dried coal. The sum of the percentage 
of surface moisture plus the percentage of moisture in air-dried 
coal is the total moisture. When making the determination for 
moisture too much care cannot be exercised to remove all of it. 

Determination for Volatile Matter. The amount of volatile 
matter in coal is determined usually with a sample as originally 
received without drying. A suitable sample should weigh about 
.0035 pound— about 1.5 grams — which should be pulverized in a 
mortar and put into a clean platinum or porcelain crucible. Then 
weigh the crucible with the coal it contains in a balance sensi- 
tive enough to weigh accurately to one-thousandth pound. 
After this weighing has been done as carefully as 'possible, 
a cover like the ones usually provided for crucibles of this 
kind is to be put on to cover it tightly. Now heat the cru- 
cible for 3^ minutes over a Bunsen burner, keeping the crucible 
at a bright red heat, and then immediately, without cooling, 
for 3^ minutes over an air-blast lamp. After cooling weigh, 
and the difference between the weighings is the sum of the 
volatile matter and the total moisture. 

Determination of Fixed Carbon. The determination of the 
fixed carbon is made by heating again the sample used for the 
determination of volatile matter. 1 Now, however, the cover 

1 If the sample tested is a bituminous coal it will be observed that 
coke has been formed by the removal of the volatile matter. 



180 POWER PLANT TESTING 

of the crucible is to be removed and heat is to be applied, 
preferably with a Bunsen burner, until all of the carbon is 
burned; that is till the weight becomes constant. If the time 
available for making the test is limited an air-blast lamp may 
be used instead of the Bunsen burner. The rate of combus- 
tion can be increased by stirring the sample from time to time 
with a platinum wire. What now remains in the crucible is 
the ash. The difference between the weight found after the 
volatile matter had been driven off and the weight of the 
crucible and the ash is the weight of fixed carbon. Weight 
of ash should be determined by weighing the crucible again 
when empty. 

If sulphur and phosphorus determinations are required 
they should be made by an expert chemist. 



CHAPTER IX 

FLUE GAS ANALYSIS 

Flue Gas Analysis. The analysis of flue gases in con- 
nection with tests of steam boilers gives a valuable means 
for determining the relative value of different methods of 
firing and of different types of furnaces. Errors in the analysis 
of flue gases are most often due to the inability to secure 
an average sample of the gases in the different parts of a flue 
or chimney. The composition is likely to vary considerably 
even during short intervals, and it is therefore desirable to 
adopt some method of sampling which will permit collecting 
the sample slowly for a considerable period. 

A very simple and convenient sampling apparatus is shown 
in Fig. 169. 

The sample of gas is taken from the flue or chimney through 
the pipe shown at the top of the figure. This pipe extends 
well into the flue and has usually a long slot cut into one of 
the sides so that a better sample of gas can be taken than if 
it were taken at the end of the pipe. The end of the pipe 
outside the flue is connected by means of a short rubber tube 
to the sampling bottle. A valve V should be put as near as 
possible to the end of such pipes, so that they can be closed 
up when the sampling bottle is removed for analysis. If a 
valve is not provided or is not closed, the suction in the flue 
will draw air into the pipe, and when again connecting up the 
sampling bottle this air must be removed before a true sample 
can be taken. The sampling bottle is preferably one with 
a wide neck, closed with a cork through which two glass tubes 
pass into the bottle, one reaching nearly to the bottom and 
the other entering only a little beyond the bottom of the cork. 
The longer tube can be connected to an aspirator or ejector, 
(Fig. 170) a water-jet exhaust or any similar device producing 
a steady suction. 

181 



182 



POWER PLANT TESTING 



Small aspirators or ejectors operating on the principle of 
an injector with a small stream of water which entrains the 

gases is very convenient 
for collecting samples con- 
tinuously. Water enters 
through a vertical nozzle, 
entrains air or gas drawn 
in through the side open- 
ings and the mixture of 
atomized water and air is 
discharged with consider- 
able velocity through the 
forcing tube at the bottom. 
If an aspirator is not 
available, the bottle may 
be filled with mercury and 
by making a siphon of the 
rubber tube attached to 
the longer of the two tubes 
in the bottle, the mercury 
can be gradually drawn 
out and gases drawn in. 
By adjusting the valve V 
the jrate of flow of the 
gases into the bottle can 
be regulated. Mercury is 
too heavy to use in a very 
large sampling bottle and 
therefore water is often 
used instead, with the dis- 
advantage, however, that 
the water will probably 
absorb some of the con- 
stituents of the gas. On 
this account very little 
water should be left in 
the bottle, with the sample 
of gas. If the water is 
saturated with gases, as it will be from long use, this precaution 
need not be observed. 




P = Pipe 
V= Valve 



Fig. 169. — Sampling Bottle for Collecting 
Flue Gas. 



FLUE GAS ANALYSIS 



183 



^1H 



The bottle and the tubes must .be completely filled with 
water before beginning to take the sample, because any air 
left in them will remain in the bottle to be mixed with the 
sample of the gas. If the end of the cork going into the bottle 
is made slightly conical it will be easier to avoid entrapping 
bubbles of air at the top of the bottle. 

This type of sampling bottle can be used also very con- 
veniently by reversing the connections, of its tubes; that is, 
by attaching the long tube to the pipe entering the flue, and 
then turning the bottle upside down. The water will then 
run out through the shorter tube and 

the gas will be drawn in to fill the Water 

bottle. 

A portion of the gas can be re- 
moved from the sampling bottle into 
the measuring burette or tube required 
for making the analysis of the flue 
gas by connecting the short tube of 
the sampling bottle to the burette or 
to some other part of the gas analysis 
apparatus as may be required. If 
now the rubber tube connected to 
the longer tube of the sampling bottle 
when disconnected is put into a pail 
well filled with water, then as the gas is 
withdrawn from the bottle, water will 
be drawn from the pail to displace it. 
One of the advantages of this appa- 
ratus is that it can be easily made 
from the materials obtainable in almost 
any town or village. A two-quart preserving jar with a rubber 
cork to fit and tubes of glass, brass or iron can be used to 
make up a very good sampling bottle. 

Since there is nearly always a great variation in the com- 
position of the gases in the various parts of a flue or chimney 
it is not very likely that a tube open at the end and having 
a long slit like the one described in the preceding paragraphs 
will give a " fair " sample. Obviously most of the gas will 
enter the slot in that portion of its length nearest the col- 
lecting apparatus. Another device often used for a sampling 



Discharge 

Fig. 170. — Water-jet As- 
pirator or Ejector. 



184 



POWER PLANT TESTING 



tube consists of a horizontal pipe into which a number of 
branch tubes are fitted. These branch tubes are arranged 
so that the openings at their ends will take samples from 
the different parts, of the flue or chimney in which they are 
placed. Sometimes these branch pipes are also slotted or are 
perforated with small holes drilled into their walls. 

Fig. 171 shows an arrangement of sampling tubes for col- 
lecting flue gas recommended by the American Society of 
Mechanical Engineers. It consists of a series of standard 

one-fourth inch pipes, 
all open and otherwise 
alike at the ends and 
of equal lengths. 
Each pipe is to be 
placed with one end 
in a shallow box or 
receiver made of gal- 
vanized sheet iron. 
It is convenient usu- 
ally to make the depth 
of this sheet -iron box 
about the same as 
that of a course of 
bricks. These tubes 
should be arranged so 
that the open ends 
will be at points well 
distributed over the 
area of the flue which 
in the figure is marked 
A. The other ends, which are also open, are to be enclosed 
in the receiver B. The receiver is connected by four tubes 
C, C with a mixing box D. The flue gases drawn from 
it should be well mixed and should represent an average 
sample from the flue of chimney from which they are 
taken. Tests have shown that two such sampling devices 
placed in the same flue one above the other about a foot 
apart, will furnish samples of the flue gases showing the same 
composition when analyzed. 

A very convenient type of sampling bottle is shown in 




Fig. 171. — A. S. M. E. Arrangement of 
Sampling Tubes for Flue Gas. 



FLUE GAS ANALYSIS 



185 



Fig. 172. It consists of a bottle with an opening at the bottom 
(tubulated), and is provided with a cork at the mouth through 
which a glass funnel F and a tube are passed. The bottle con- 
tains water and light oil, and when it is filled there will be a 
layer of about 4 inches of the oil over the water. The tube O 
at the top is to be connected to the sampling tubes in the 
flue and the sample is taken in by opening the valve in this 
tube and also the one at the bottom of the bottle. The 
water drains off at the bottom and is replaced by the 
sample of gas. The glass funnel is used for pouring water 
into the bottle and in this way expelling the gas needed for 
analysis. The gas is thus made to pass 
out through the same tube through 
which it is drawn in. 

Another type of sampling apparatus 
used by many engineers consists of two 
galvanized-iron tanks, each about 2 
feet high, and about 5 inches in diam- 
eter. On the side of each of these 
tanks and close to the bottom a valve 
is attached by soldering. These two 
valves are connected by a piece of 
heavy rubber tubing. One of the 
tanks is closed at the top, and a 
small stopcock or valve is attached to 
the cover. The other tank is open at the 
top. The apparatus is used for collect- 
ing gas by filling to ' ' overflowing ' ' the tank with the closed top 
with water from the other tank by raising the latter so that 
the level of the water in it is above that of the water in the 
closed tank. By means of rubber tubing the stopcock or 
valve on the closed tank is then connected to the sampling 
tubes in the chimney or flues. Meanwhile the open tank is 
held at such an elevation that the water will not run back 
into it and create a vacuum in the closed tank. After this 
connection has been made the stopcock and valves are to be 
opened again, so that when the open tank is placed below 
the level of the closed one, the water will flow into the open 
tank and fill the other one with gas. This operation should 
be repeated several times before the sample is carried away 




Fig. 172. — Another Type 
of Sampling Bottle. 



186 POWER PLANT TESTING 

to be analyzed, so that there can be no doubt that none of 
the air in the sampling tubes entered the sample to be analyzed. 
This water can be used over and over again, and when it has 
become saturated with gas it is practically as good as mercury 
for use in collecting the gases. 

When a sample of flue gas is taken from the flue at a 
considerable distance from the furnace it is likely to become 
mixed with air leaking through the brickwork of the boiler 
setting, and the analysis will not show the true relations between 
the volumes of the so-called flue gases and the excess of air. 
To prevent as much as possible this leakage of air the joints 
in the masonry must be examined and repaired if necessary 
and the sample must be taken as near as possible to the fire, 
bearing in mind, however, that they must be drawn very 
slowly from the hot flue in order that they will be cooled down 
gradually to avoid dissociation. For hot gases an earthen- 
ware collecting vessel may be used if a glass bottle is likely 
to be broken. If dissociation occurs in the sample the analysis 
may show results entirely different from the true composition 
of the gas in the flue. It is also difficult to prevent the 
entrance of air into a flue through the bearings of dampers, 
and whenever it is possible the sample of flue gas should be 
obtained between the furnace and the damper. At high tem- 
peratures sampling tubes of other metals than platinum 1 or 
nickel are not quite satisfactory, since by their oxidation they 
abstract the oxygen from the gases passing through them. 

Apparatus for the Analysis of Flue Gases. Samples of 
flue gases contain in varying amounts carbonic dioxide (car- 
bonic acid), oxygen, carbonic oxide, nitrogen, unburned hydro- 
carbons, and occasionally some free hydrogen. For the data 
which an 'engineer usually requires it is not necessary to deter- 
mine by direct analysis more than three of these; carbonic 
dioxide, C0 2 , oxygen, 2 , and carbonic oxide, CO. 

The determination of carbonic oxide, CO, with the facilities 
and the portable apparatus ordinarily available in engineering 
laboratories is often somewhat doubtful. Some authorities 
state that there is rarely more than a trace of carbonic oxide 
to be found in the gases from combustion in the ordinary 

1 Porcelain and annealed glass are also satisfactory materials to use 
for making sampling tubes for very hot flues. 



FLUE GAS ANALYSIS 



187 



types of furnaces. When more than one per cent of carbonic 
oxide is shown by the analysis and the carbonic dioxide deter- 
mination is not over 14 per cent, it may usually be 
assumed that a large part of what is taken to be carbonic 
oxide is oxygen which was not absorbed by the proper reagent. 
In the following table a set of analyses of flue gases is 
shown. The determinations were made by Scheurer-Kestner 
with coal from Ronchamp. Other analyses of flue gases may 
be checked by a comparison with this table. Thus when the 
analysis shows about 8.2 per cent CO2, the sum of the per- 
centages of C0 2 and 2 will probably be between 19 and 20. 

PERCENTAGE COMPOSITION OF FLUE GAS 



C0 2 


O2 


CO 


N 


Hydrocarbons 


8.2 


"•3 


. 2 


79.8 


•5 


10.8 


9.0 


. 2 


79-7 


•3 


12.9 


5-5 


. 2 


80.3 


1 . 1 


13-4 


4-4 


. 2 


80.2 


1 .8 


14.6 


2.8 


■3 


80.6 


1.7 



In the portable apparatus used by engineers for the analysis 
of flue gases a separate pipette or treating tube is provided 
for each reagent, and the chemicals used are of greater strength 
than the reagents used by some chemists. The following 
reagents give satisfactory results in a portable apparatus: 

(1) For absorbing CO2 a solution of one part of potassic 
hydrate (KOH) or caustic potash dissolved in two parts by 
weight of water is generally used. 

(2) For absorbing 2 either an alkaline solution of pyro- 
gallic acid or sticks of phosphorus are employed. 

The alkaline solution of pyrogallic acid is prepared by 
mixing together preferably in the absorption pipette or treating 
tube, to prevent access of air, 5 grams of pyrogallic acid 
powder and 100 cubic centimeters of potassic hydrate (KOH) 
solution prepared as explained above. 1 

(3) For absorbing carbonic oxide a hydrochloric acid solu- 
tion of cuprous chloride is used. This is prepared by dis- 
solving about 10 grams of cupric oxide in from 100 to 200 

1 When the temperature is lower than about 55 degrees Fahrenheit 
this reagent does not give satisfactory results. 



188 



POWER PLANT TESTING 



cubic centimeters of concentrated hydrochloric acid. This 
solution must be allowed to remain in a bottle tightly closed 
and well filled with copper wire or gauze, until the cupric 
chloride is reduced to cuprous chloride. In this latter state 
the liquid will be colorless. Exposure to the air produces a 

brown color, indicating 
the cupric state. 

After a time these 
reagents must be re- 
placed by new solu- 
tions. The potassium 
hydrate solution may 
be used till each vol- 
ume has absorbed forty 
volumes of C0 2 . Py- 
rogallic acid solution 
deteriorates rapidly 
and each volume 
should be expected to 
absorb only one or 
two volumes of O2. 
Cuprous chloride will 
absorb an equal volume 
of CO. 

Portable devices for 
the analysis of flue 
gases are generally 
known as " Orsat " 
apparatus. Of these 
there are various types. 
The one devised by 
Fisher, shown in Fig. 173, has been used extensively. It 
consists of a measuring-tube M surrounded by a water- 
jacket, and set of absorption pipettes, A, B, C, each filled 
with a reagent. Each of these pipettes (Fig. 174) consists 
of two glass vessels connected by a U-shaped glass tube at 
the bottom. One end of these pipettes is joined by means 
of a short piece of rubber tubing to a glass yoke T, which 
is designed for attachment at one end e to a tube leading 
to the sampling-bottle and at the other end to the measuring- 




Fisher's "Orsat" Apparatus. 



FLUE GAS ANALYSIS 



189 



tube M. A water bottle W is connected by a flexible rubber 
tube P to the bottom of the measuring tube. 

Before a sample of gas is taken into the apparatus for 
analysis certain adjustments must be made. In the first 
place, the reagents in the pipettes must all be brought to a 
standard level at some arbitrary point, usually indicated by 
a scratch on the glass tube just below the short rubber tube 
connecting it to the yoke. This adjustment is accomplished 
by opening one at a time the valves at the tops of the pipette 
and removing the air (or the gas as 
the case may be) from it by lowering 
the water level in the measuring 
tube. The position of the water 
bottle determines, of course, the 
level of the water in the measuring 
tube. When all the air and gases 
remaining from a previous test have 
been expelled from the apparatus 
by filling the measuring tube and 
the tubes comprising the yoke with 
water, one of the tubes in the 
sampling bottle should be connected 
to the apparatus at e and by opening 
the valve in the yoke at that end 
and lowering gradually the level of 
the water in the measuring tube M 
a sample is obtained for analysis. 
This sample must be measured by 
the scale on the measuring tube at 
atmospheric pressure 1 to the nearest 
tenth of a cubic centimeter. 2 After 

the measurement has been made and recorded if the cock in the 
tube leading to the absorption pipette containing the reagent for 
absorbing C0 2 is opened and then the water bottle is raised, 
all of the measured sample of gas can be forced over into 




Fig. 



174. — Pipette of Fisher's 
"Orsat" Apparatus. 



1 The pressure of the gas is " atmospheric " when the water bottle 
is held so that the water in it and that in the measuring tube are at the 
same level. 

2 The scales of practically all measuring tubes used for gas analysis 
apparatus are graduated in cubic centimeters. 



190 POWER PLANT TESTING 

the pipette. The reagent acts more rapidly on the gas if the 
water bottle is raised and lowered a few times. This movement 
of the water in the measuring tube agitates the gas and also the 
reagent and exposes more of the gas to the direct action of the 
absorbent. To increase the surface over which the reagents can 
act, the pipettes are filled with small glass tubes. When the gas 
has been in the first pipette for about a minute, it should be drawn 
back into the measuring tube with the level of the reagent 
brought back to the mark where it was originally, and the cock 
closed. The pressure of the gas is again made atmospheric 
and its volume measured. Now repeat this operation until 
two or three measurements are obtained which are alike, 
showing that all the CO2 has been absorbed. Then the cock 
on the tube leading to the pipette containing the absorbent 
for oxygen can be opened, the gas forced over, and measured 
several times till a constant volume is observed. Finally the 
gas is passed into the third pipette for absorbing CO, repeating 
the operation of measuring as with the other pipettes. 

The absorption of oxygen will usually require considerably 
more time than for the determinations of the carbonic acid 
(C0 2 ) and the carbonic oxide (CO), so that it is unnecessary to 
make a measurement of the volume of the gas till after the 
gas has been exposed about three minutes to the reagent. 
Soft rubber bags (see Fig. 174) should be attached by means 
of glass tubes to the corks shown in the pipettes on the farther 
side in Fig. 173 and are provided to protect the reagents from 
absorbing oxygen and carbonic oxide from the air. Both of 
these reagents will absorb oxygen from atmospheric air, so 
that the access of fresh air must be prevented. The rubber 
bags are useful also for the purpose of producing alternately, 
with the pressure of the hand, suction and pressure for agitating 
the reagents. 

A form of Orsat apparatus particularly suitable for portable 
use, and in which renewals of broken parts can be cheaply and 
easily made, is illustrated in Fig. 175. This apparatus, designed 
by Professor John R. Allen and the author, 1 is also particularly 
suitable for the use of engineers because the pipettes containing 
the reagents can be removed from the apparatus very easily 

1 Made commercially by the Bausch & Lomb Co., Rochester, N. Y. 



FLUE GAS ANALYSIS 



191 



tor changing solutions. They can be emptied, refilled, and 
replaced in a very short time. The absorption pipettes (Fig. 
176) are made simply of two glass test-tubes, the smaller one 
inside the larger one. The small test-tube is held as it were 
inverted, and has a glass " capillary " tube fused into its closed 
end. The outer tube is closed at the top by a rubber stopper 
through which the capillary portion of the inner tube passes. 
Very small glass tubes are placed in the inner test-tube to 




Fig. 



75. — Allen-Moyer Gas 
Apparatus. 



Fig. 176. — Absorption Pipette of 
Allen-Moyer Gas Apparatus. 



increase the surface for the action of the reagent. The pipette 
is held in place 'by means of a hard-rubber disk supported on 
brass screws. The level of the reagent in the pipette is estab- 
lished when the air in the inner tube is drawn out and the level 
of the liquid rises to a mark on the glass capillary tubes. In 
the ustial forms of the Orsat apparatus the pipettes invariably 
become leaky at the stopper provided for emptying. In the 
Allen-Moyer apparatus there is no opportunity for such leakage. 
When the sample of the gas is passed through the capil- 
lary tube into the inner test-tube, the reagent is displaced 



192 POWER PLANT TESTING 

and raises the level in the outer test-tube. Similarly when the 
gas is passed back into the measuring tube the level falls in 
the outer tube, rises in the inner one, and is brought back to 
the original level at the mark on the capillary tube. Otherwise 
the method of operation is the same as described for Fisher's 
apparatus (Fig. 174). 

In this apparatus the measuring tube M and water bottle 
W are of the same type as those used in Fisher's design. The 
yoke is also similar, although usually made of hard rubber to 
avoid breaking it in transportation. It has also spring pinch- 
cocks instead of ground-glass cocks. When glass cocks are 
used by inexperienced persons all sorts of difficulties are likely 
to result, particularly that it often happens that they are not 
pressed into their seats tightly enough to prevent the loss of 
gas or the entrance of air. Sometimes the glass cocks will 
be put into their seats so tightly that it is impossible to 
move them without breaking. These difficulties, although 
met often enough in laboratory work, are still more frequently 
observed in practice. 

Coefficient of Dilution. The coefficient of dilution is the 
ratio of the volume of the air supplied to the volume theoreti- 
cally necessary to provide the oxygen required for combustion. 
It will now be shown how this coefficient can be calculated from 
an analysis of the flue gases. 

Oxygen when combining with carbon to form carbonic 
dioxide produces a volume equal to itself, thus, 

c+o 2 =co 2 , 

and in forming carbonic oxide produces twice the volume 

2C+0 2 = 2C0. 

Now if we use symbols to designate the percentages by volume 
of the gases in a sample of flue gas as follows : 

a is the percentage by volume C0 2 , 

b is the percentage by volume 2; 

c is the percentage by volume CO, 

d is the percentage by volume N (nitrogen). 

Then the volume occupied by the free oxygen in the air 
before combining with the carbon was a+b+|c per cent, 
while that required is obviously a+lc per cent. 



FLUE GAS ANALYSIS 193 

The coefficient of dilution is therefore, 

a + b + |c 

-TJ+- •••;••• (53) 

In a little different form the reactions given in the last 
paragraph may be stated (i) for carbon burned to CO2, 

2C + 20 2 = 2C0 2 , (54) 

(2 vols.) (2 vols.) (2 vols.) 
24 64 88 

and (2) for carbon burned to CO, 

2C + 2 = 2CO. ..... (55) 

(2 vols.) (1 vol.) (2 vols.) 

24 32 56 

The ratio of the volume of the carbon vapor burned to CO2, 
to the volume burned to CO is the same as the ratio of the 
volume of CO2 in the products of combustion is to the volume 
of CO. Further since the ratio of volumes of the carbon 
vapor is obviously the same as the ratio of the corresponding 
weights, we may say that in a mixture of gases, the ratio of 
the weight of carbon required to produce the C0 2 to the weight 
needed for the CO is equal to the ratio of the volume of C0 2 
in the mixture to the volume of CO. 

The atomic weights of carbon and oxygen show (equation (54)) 
that a volume of oxygen is 2§ (64/24) times as heavy as an equal 
volume of carbon vapor. It follows then that for burning one 
pound of carbon to CO2, 2§ pounds of oxygen are required. 
The other reaction (55) showing the combination of carbon and 
oxygen to form CO shows with the same reasoning that 1^ 
pounds of oxygen are required to burn one pound of carbon 
to CO. 

In the general case we are considering and using symbols 
a and c respectively as before to represent the volumes of C0 2 
and of CO in the flue gases, then the weight of the carbon burned 

to C0 2 is to the weight burned to CO as a is to c and if 

a +c 

Q 

represents the weight of carbon burned to C0 2 and the 

a -He 



194 POWER PLANT TESTING 

weight burned to CO, then the weight of oxygen required per 

pound of carbon is 2§( ) + I 3\ ) and the weight of air 1 

per pound of carbon is in pounds, 

f hfc)+^fc)] (56) 

If z is the percentage by weight of carbon then the weight 
of air in pounds per pound of coal is 

^K^c+'^c)}- •■■■■' W 

Volumetric analyses of the flue gases can be used also to 
calculate the weight of the products of combustion (flue gases) 
per pound of coal burned and also the heat units lost in these 
gases. For this calculation the relations of the molecular 
weights are important. 

Molecular weight of 



co 2 = 


= 44 


2 = 


= 32 


co = 


= 28 


N 2 = 


= 28 


c = 


= 12 



Now in a sample of x pounds of flue gases in which the 
percentages by volume are represented by the symbols a, b, 
c, d, the relative percentages by weights of the constituents 
will be 



co 2 = 


44a. 
x ' 


2 = 


= 32b. 
X 


co = 


28C_ 
X ' 


N 2 = 


2 8d_ 

X 



and we can write further 

1 Weight of air may be checked with Peabody's and Jacobus' equa- 
tions (61, 62 and 63 1 ), pages 225-228. 



FLUE GAS ANALYSIS 195 

Weight of carbon burned to CO2 in x pounds of gas 

1 ^ 
= — X44a= 12a. 

44 

Weight of carbon burned to CO in x pounds of gas 



Total weight of carbon burned in x pounds of gas= 1 2 (a +<;). 

Total weight of carbon burned per pound of gas = 12 -. 

x 
Total weight of gas generated per pound of carbon 



(a+c) 

Of this total weight of gas as expressed by the last equa- 
tion the constituents are distributed in percentages by weight 
as follows : 

Weight of CO2 in samples per pound carbon burned, 

44a. x 



or we may write 



and similarly, 



ixj X - 


123 


■■(a+c)' 




co 2 = 


= W\ 


44a 
12(0+1 


- lb . 


o 2 = 


=w 2 


- ft , ib -^ 

1 2 (a+c) 


co = 


= wz -■ 


28c n. 
1 2 (a + c) 


N 2 = 


= w 4 -- 


2&d 


-lb 



i2 (a+c) 



Total weight of gases iv g per pound of coal burned, if 
there is z per cent ? of carbon in the coal, is in pounds 

2(440 + 326 + 28c + 28d) 

w e = -, (58) 

g 1 2 (a +c) 100 ° ; 

1 It may be assumed for very approximate values that z= i — y where y 
is the per cent of ash in the coal. 



196 POWER PLANT TESTING 

Now if we represent by t f and t a the temperatures respect- 
ively in degrees Fahrenheit of the gases in the flue and of 
the air entering the furnace, then the heat lost in the flue 
gases Q g per pound of coal is, inserting values of specific 
heats, l 

Q == (.2IJWi + .2I']W2+.245W 3 +.244W 4 )(t i -Q. 

fi IOO 

The total heat generated Q by the more or less incomplete 
combustion of one pound of coal when there are a and c per- 
centages by volume respectively of CO2 and CO in the flue 
gas is 

Qo =— (-^7X14,600+-^- X 44 oo)(B.T.U,). . (59) 
ioo\a+c a +c / 

Since the heat of combustion of carbon when burned to C0 2 

is approximately 14,600 and when burned to CO is about 

4400 B.T.U. 

Finally, if Q p is the heat from perfect combustion or the 

" calorific " value in B.T.U. of a pound of coal, then the efficiency 

Q 
of the furnace 2 = — . The percentage of heat from perfect com- 

~p 

(i 
bustion lost in the flue gases =— . 

Qp 

Recording Apparatus for Determining C0 2 . A typical 
apparatus for making a continuous record of the percentage by 
volume of carbonic dioxide in gases is shown in Fig. 177. The 
gas is taken to the instrument from the side flue or last com- 
bustion chamber of each boiler or furnace to the inlet pipe D 
and is drawn through the machine by a special water aspirator 
0, fixed to the top of the instrument by means of the standard 
T. After actuating the aspirator 0, a portion of the water flows 
to the small tank L, which serves as a pressure regulator, and is 
provided with an overflow tube R. From this tank the water 

1 This method of finding the heat escaping in the flue gases can be 
used to correct determinations made with the Junkers calorimeter (page 
i-7 6) when the products of combustion are discharged at a temperature 
different from that of the rodm. 

2 For the calculation of related quantities see "Heat Balance" (A.S. 
M.E. Rules), page 214; also Allen and Bursley's Heat Engines, pages 64-65, 



FLUE GAS ANALYSIS 



197 



enters the tube H in a fine stream, which is adjusted by the 
cock 5 and gradually fills the vessel K. This vessel consists of 
an upper and a lower compartment, the two being in communi- 
cation through a tube erected in the upper chamber and reaching 
nearly to the top. Water, which enters this vessel K through 
the tube //, gradually fills the upper chamber and thus com- 
presses the air contained in it. This pressure is transmitted to 
the lower compartment through the communication tube 
mentioned above, and acts upon 
the mixture of glycerine and water 
with which this is filled, driving it 
out into the calibrated tube .C. 
When the rising liquid in C has 
reached the inlet and outlet to 
this vessel, no more gas can enter 
the calibrated tubes and the aspira- 
tor will now draw the gas through 
the seal F. 

Before the liquid can close the 
central tube in C, the gas must 
overcome the slight resistance 
offered by the elastic bag P, and 
is thereby forced to assume atmos- 
pheric pressure. When the liquid 
has sealed the lower open end of 
this central tube, exactly ico 
cubic centimeters of flue gas are 
trapped off in the outer vessel 
C and its companion tube, under 
atmospheric pressure. As the 
liquid rises, the gas is forced 
through the thin tube Z into the 
vessel A, which is filled with a 
solution of caustic potash for absorbing carbonic dioxide. 

The gas remaining gradually displaces the potash solution 
in A, sending it up into the vessel B. This has an outer jacket, 
filled with glycerine and supporting a float N. Through the 
center of this float reaches a thin tube, through which the air 
in B is kept at atmospheric pressure. The float is suspended 
from the pen gear M by a silk cord and counter-balanced by the. 




Fig. 



177. — Recording C0 2 
Apparatus. 



198 



POWER PLANT TESTING 



weight X. The liquid in B forces a portion of the air through 
the central tube in the float, and then raises the latter, causing 
the pen lever to swing upward, carrying the pen, Y, with it. 

The mechanism is so calibrated and adjusted that the pen 
will travel to the top, or zero line, on the chart when only- 
atmospheric air is passing through the machine, and nothing 
is absorbed by the potash in A. When there is any carbonic 
dioxide in the gas it is absorbed by the potash in A, and not 
so much of this liquid would be forced up into the vessel B. 



.A4 ^ 




From Boikr Flee 



Fig. 178. — C0 3 "Weighing" Apparatus (Econometer). 



The float would not then cause the pen to travel up so high on 
the chart, in proportion to the amount of CO2 absorbed. 

Another apparatus for making continuous determinations 
of C0 2 in flue gases is shown in Fig. 178. Gas from the boiler 
flue enters at M , passes through an excelsior filter where dust is 
removed, and then goes on through tubes leading it through 
glass vessels containing cotton wool and calcium chloride. 
After being cleaned it passes in the direction of the arrows 
through the valve B into the weighing apparatus. On account 
of the greater specific gravity of C0 2 the larger the percentage 
of this gas the greater the tendency will be to pull downward 



FLUE GAS ANALYSIS 199 

the vessel G so that the pointer 5 on the balance can be adjusted 
to make the scale over which it travels indicate the percentage 
of CO2. For such a method of determination, obviously, the 
gas must be clean and dry. The cleaning is done by the excelsior 
and wool filters and the drying is done by the calcium chloride. 



CHAPTER X 

BOILER TESTING 

Tests of steam boilers are made to determine usually the 
following principal results : 

(i) Quantity of steam evaporated or furnished per hour. 

(2) Efficiency as a heat user, or weight of water evap- 
orated per pound of combustible (fuel less moisture and ash) . 

(3) Weight of water evaporated per hour per square foot 
of water-heating surface. 

(4) Weight of fuel burned per hour per square foot of 
grate surface. 

Leakages of any kind are always a lurking enemy for those 
engaged in any kind of accurate testing, and work with boilers 
is no exception. Poor results with boilers are due more often 
to air leakage than to any other fault. Air entering the 
setting and flues instead of the furnace does not assist com- 
bustion, but, on the contrary, absorbs from the hot gases a 
quantity of heat which otherwise might pass through the 
boiler-heating surfaces into the water in the boiler. When 
the object of a series of tests "is, for example, to compare one 
kind of coal with another, or one type of grate or mechanical 
stoker with another, the losses due to air leakage would not 
be of much consequence in what 'are only comparative results; 
but if a boiler is to give the best possible efficiency and capacity, 
air leaks must be stopped. 

In practice the importance of closing air leaks in the boiler 
setting is forcefully presented when patented devices for fuel 
saving are installed in boiler plants. Important economies 
in many cases are guaranteed if the new device is adopted, and 
then the claims of the agent are made good by instructing his 
workmen to go over the boiler, closing up all cracks in the 
setting through which cold air could enter, and at the same 

200 



BOILER TESTING 201 

time covering the outside surface of the setting with a coating 
impervious to air. By such means the owner of the plant 
pays a high price for results that could have been obtained 
much more cheaply. 

The first of the principal objects of a boiler test stated 
above is to determine its capacity " rating." 1 The unit of 
capacity most generally used in steam boiler practice is the 
" boiler " horse power. Now this term horse power has two 
very distinct meanings in engineering practice. Usually it is 
taken to mean the rate of doing work or the work done in a 
definite period of time. In this sense it means, as in the case 
of engines, turbines, water-wheels, etc., 33,000 foot-pounds 
per minute. 2 In the case of a steam boiler, however, where the 
work done must be measured by the conversion of water into 
steam, a horse power is taken as the evaporation of 30 pounds 
of water at a temperature of 100 degrees Fahrenheit into 
steam at 70 pounds pressure above the atmosphere. When 
this unit was adopted it was considered that 30 pounds per 
hour was approximately the requirement per indicated horse 
power of an average engine. The Committee on Boiler Tests 
of the American Society of Mechanical Engineers (page 218) 
have adopted what is in effect the same unit, stating it, how- 
ever, somewhat differently — that a boiler horse power is equiv- 
alent to evaporating 34.5 pounds of steam per hour from feed- 
water temperature of 212 degrees Fahrenheit into steam at the 
same temperature. According to the latest steam tables this is 
equivalent to approximately 33,480 B.T.U. per hour, or 558 
B.T.U. per minute. 

Unit of Evaporation. For reducing the results of the boiler 
tests to a common standard the term "unit of evaporation" 
is used. It is the heat required to evaporate a pound of water 



1 When the steam supply is small or if, for any reason, the noise due 
to escaping steam from the calorimeters used is objectionable, a calorim- 
eter may be shut off sometimes between readings. The length of time 
the calorimeter is in operation must then be carefully noted in order to 
determine the weight of steam lost through it by calculating the flow 
through its orifice (see page 148). The flow of steam, however, through 
the calorimeter must always be started before observations of the tem- 
peratures are to be taken in order to get constant conditions. 

2 This unit of horse power was adopted by James Watt, who considered 
it equivalent to the work done by a good London draft horse. 



202 



POWER PLANT TESTING 



from and at 2 1 2 degrees Fahrenheit, which according to standard 
steam tables is approximately equivalent to 970.4 B.T.U. 1 

Graphical Log Sheets of boiler tests similar to the one 
shown in Fig. 179 are very serviceable for checking the obser- 
vations when made during the test as the data are taken. In 




Fig. 179. — Graphical Chart of a Boiler Trial. 



the report of a test it shows also the relative irregularity or 
regularity of the conditions affecting the results. 

Standard Methods for Boiler Trials. The American Society 
of Mechanical Engineers has adopted rules for conducting 
boiler trials which are generally accepted in America and are 
also considered with favor in England. 2 These rules are so 
complete that they will be given here with practically no 
abridgement. 3 

1 Marks and Davis' Steam Tables and Diagrams, see also Peabody's 
Steam Tables, 1909 Edition. 

2 Engines and Boilers by W. W. F. Pullen, pages 466-475. 

3 Transactions American Society of Mechanical Engineers, vol. 31, 
pages 34-1 1 1 (including discussions). 



BOILER TESTING 203 

RULES FOR CONDUCTING BOILER TRIALS 
ABRIDGED CODE OF 1899. 

I. Determine at the outset the specific object of the pro- 
posed trial, whether it be to ascertain the capacity of the 
boiler, its efficiency as a steam generator, its efficiency and 
its defects under usual working conditions, the economy of 
some particular kind of fuel, or the effect of changes of design, 
proportion or operation; and prepare for the trial accordingly. 

II. Examine the boiler, both outside and inside; ascertain 
the dimensions of grates, heating sufaces, and all important 
parts; and make a full record, describing the same, and 
illustrating special features by sketches. The area of heating 
surface is to be computed from the surfaces of shells, tubes, 
furnaces, and fire boxes in contact with the fire or hot gases. 
The outside diameter of water tubes and the inside diameter 
of fire tubes are to be used in the computation. All surfaces 
below the mean water level which have water on one side 
and products of combustion on the other are to be considered 
as water-heating surface, and all surfaces above the mean 
water level which have steam on one side and products of 
combustion on the other are to be considered as superheating 
surface. 

III. Notice the general condition of the boiler and its equip- 
ment, and record such facts in relation thereto as bear upon 
the objects in view. 

If the object of the trial is to ascertain the maximum 
economy or capacity of the boiler as a steam generator, the 
boiler and all its appurtenances should be put in first-class con- 
dition. Clean the heating surface inside and outside, remove 
clinkers from the grates and from the sides of the furnace. 
Remove all dust, soot, and ashes from the chambers, smoke 
connections, and flues. Close air leaks in the masonry and 
poorly fitted cleaning doors. See that the damper can be opened 
wide and closed tightly. Test for air leaks by firing a few 
shovelsful of smoky fuel and immediately closing the damper, 
observing the escape of smoke through the crevices, or by 
passing the flame of a candle over cracks in the brickwork. 



204 POWER PLANT TESTING 

IV. Determine the character of the coal to be used. For 
tests of the efficiency or capacity of the boiler for comparison 
with other boilers the coal should, if possible, be of some kind 
which is commercially regarded as a standard. For New 
England and that portion of the country east of the Alle- 
gheny Mountains, good anthracite egg coal, containing not 
over 10 per cent of ash, and semi-bituminous Clearfield (Pa.), 
Cumberland (Md.), and Pocahontas (Va.) coals are thus regarded. 
West of the Allegheny Mountains, Pocahontas (Va.) and New 
River (W. Va.) semi-bituminous, and Youghiogheny or Pitts- 
burg bituminous coals are recognized as standards. 1 There 
is no special grade of coal mined in the Western States which 
is widely recognized as of superior quality or considered as 
a standard coal for boiler testing. Big Muddy lump, an Illinois 
coal mined in Jackson County, 111., is suggested as being of 
sufficiently high grade to answer these requirements in districts 
where it is more conveniently obtainable than the other coals 
mentioned above. 

For tests made to determine the performance of a boiler 
with a particular kind of coal, such as may be specified in 
a contract for the sale of a boiler, the coal used should not 
be higher in ash and in moisture than that specified, since 
increase in ash and moisture above a stated amount is apt 
to cause a falling off of both capacity and economy in a greater 
measure than the proportion of such increase. 

V. Establish the correctness of all apparatus used in the 
test for weighing and measuring. These are : 

i . Scales for weighing coal, ashes, and water. 

2. Tanks, or water meters for measuring water. Water 
meters, as a rule, should only be used as a check on other 
measurements. For accurate work, the water should be 
weighed or measured in a tank. 

3. Thermometers and pyrometers for taking temperatures 
of air, steam, feed- water, waste gases, etc. 

4. Pressure gages, draught gages, etc. 

The kind and location of various pieces of testing appa- 

1 These coals are selected because they are about the only coals which 
possess the essentials of excellence of quality, adaptability of various 
kinds of furnaces, grates, boilers, and methods of firing, and wide dis- 
tribution and general accessibility in the markets. 



BOILER TESTING 205 

ratus must be left to the judgment of the person conducting 
the test; always keeping in mind the main object, i.e., to 
obtain authentic data. 

VI. See that the boiler is thoroughly heated before the trial 
to its usual working temperature. If the boiler is new and 
of a form provided with a brick setting, it should be in regular 
use at least a week before the trial, so as to dry and heat the 
walls. If it has been laid off and become cold, it should be 
worked before the trial until the walls are well heated. 

VII. The boiler and connections should be proved to be 
free from leaks before beginning a test, and all water connec- 
tions, including blow and extra feed pipes, should be discon- 
nected, stopped with blank flanges, or bled through special 
openings beyond the valves, except the particular pipe through 
which water is to be fed to the boiler during the trial. During 
the test the blow-off and feed-pipes should remain exposed 
to view. 

If an injector is used, it should preferably receive steam 
directly through a felted pipe from the boiler being tested. 1 

If the water is metered after it passes the injector, its 
temperature should be taken at the point where it leaves the 
injector. If the quantity is determined before it goes to the 
injector, the temperature should be determined on the suction 
side of the injector, and if no change of temperature occurs 
other than that due to the injector, the temperature thus 
determined is properly that of the feed water. When the 
temperature changes between the injector and the boiler, as 
by the use of a heater or by radiation, the temperature at 
which the water enters and leaves the injector and that at 
which it enters the boiler should all be taken. In that case, 
the weight to be used is that of the water leaving the injector 
computed from the heat units if not directly measured, and 
the temperature, that of the water entering the boiler. 

1 In feeding a boiler undergoing test with an injector taking steam 
from another boiler, or from the main steam pipe from several boilers, 
the evaporative results may be modified by a difference in the quality 
of the steam from such source compared with that supplied by the boiler 
being tested, and in some cases the connection to the injector may act 
as a drip for the main steam pipe. If it is known that the steam from 
the main pipe is of the same pressure and quality as that furnished by 
the boiler undergoing the test, the steam may be taken from such main 
pipe. 



206 POWER PLANT TESTING 

Let w =weight of water entering the injector, pounds. 

x = weight of steam entering the injector, pounds. 

hi =heat units per pound of water entering injector. 

h2 =heat units per pound of steam entering injector. 

h 3 =heat units per pound of water leaving injector. 

Then, w + x=weight of water leaving injector. 

I13 — hj 

X=Wr^— j- 1 . . . . . . 

n 2 — n H 



(60) 



See that the steam main is so arranged that water of con- 
densation cannot run back into the boiler. 

When coal is used for fuel it is usually weighed in wheel- 
barrows which can be pushed upon large platform scales. 
The time when beginning to fire from each loaded wheel- 
barrow should be noted. 

VIII . Duration of the Test. — For tests made to ascertain either 
the maximum economy or the maximum capacity of a boiler, 
irrespective of the particular class of service for which it is 
regularly used, the duration should be at least 10 hours of 
continuous running. If the rate of combustion exceeds 25 
pounds of coal per square foot of grate surface per hour, it 
may be stopped when a total of 250 pounds of coal has been 
burned per square foot of grate. 

In cases where the service requires continuous running for 
the whole 24 hours of the day, with shifts of firemen a number 
of times during that period, it is well to continue the test for 
at least 24 hours. 

When it is desired to ascertain the performance under the 
working conditions of practical running, whether the boiler be 
regularly in use 24 hours a day or only a certain number of 
hours out of each 24, the fires being banked the balance of the 
time, the duration should not be less than 24 hours. 

IX. Starting and Stopping a Test. — The conditions of the 
boiler and furnace in all respects should be, as nearly as pos- 
sible, the same at the end as at the beginning of the test. The 
steam pressure should be the same; the water level the same; 
the fire upon the grates should be the same in quantity and 
condition, and the walls, flues, etc., should be of the same 
temperature. Two methods of obtaining the desired equality 



BOILER TESTING 207 

of conditions of the fire may be used, viz., " the standard 
method " and " the alternate method," the latter being em- 
ployed where it is inconvenient to make use of the standard 
method. 1 

X. Standard Method of Starting and Stopping a Test. — Steam 
being raised to the working pressure, remove rapidly all the 
fire from the grate, close the damper, clean the ash pit, and 
as quickly as possible start a new fire with weighed wood and 
coal, noting the time and the water level 2 while the water 
is in a quiescent state, just before lighting the fire. 

At the end of the test remove the whole fire, which has 
been burned low, clean the grates and ash pit, and note the 
water level when the water is 'in a quiescent state, and record 
the time of hauling the fire. The water level should be as 
nearly as possible the same as at the beginning of the test. 
If it is not the same, a correction should be made by com- 
putation, and not by operating the pump after the test is 
completed. 

XL Alternate Method of Starting and Stopping a Test, — The 
boiler being thoroughly heated by a preliminary run, the fires 
are to be burned low and well cleaned. Note the amount of 
coal left on the grate as nearly as it can be estimated; note 
the pressure of steam and the water level. Note the time, 
and record it as the starting time. Fresh coal which has been 
weighed should now be fired. The ash pits should be thor- 
oughly cleaned at once after starting. Before the end of the 
test the fires should be burned low, just as before the start, 
.and the fires cleaned in such a manner as to leave a bed of 
coal on the grates of the same depth, and in the same condition, 
as at the start. When this stage is reached, note the time and 
record it as the stopjDing time. The water level and steam 

1 The Committee concludes that it is best to retain the designations 
" standard " and " alternate," since they have become widely known 
and established in the minds of engineers and in the reprints of the Code 
of 1885. Many engineers prefer the " alternate " to the " standard " 
method on account of its being less liable to error due to cooling of the 
boiler at the beginning and end of a test. 

2 The gage-glass should not be blown out within an hour before the 
water level is taken at the beginning and end of a test, otherwise an error 
in the reading of the water level may be caused by a change in the tem- 
perature and density of the water in the pipe leading from the bottom 
of the glass into the boiler. 



208 POWER PLANT TESTING 

pressures should previously be brought as nearly as possible 
to the same- point as at the start. 

XII. Uniformity of Conditions. — In all trials made to 
ascertain maximum economy or capacity, the conditions should 
be maintained uniformly constant. Arrangements should be 
made to dispose of the steam so that the rate of evaporation 
may be kept the same from beginning to end. This may be 
accomplished in a single boiler by carrying the steam through 
a waste steam pipe, the discharge from which can be regulated, 
as desired. In a battery of boilers, in which only one is tested, 
the draft may be regulated on the remaining boilers, leaving 
the test boiler to work under a constant rate of production. 

Uniformity of conditions should prevail as to the pressure 
of steam, the height of water, the rate of evaporation, the 
thickness of fire, the times of firing and quantity of coal fired 
at one time, and as to the intervals between the times of 
cleaning the fires. 

The method of firing to be carried on in such tests should 
be dictated by the expert or person in responsible charge of 
the test, and the method adopted should be adhered to by 
the fireman throughout the test. 

XIII. Keeping the Records.— Take note of every event con- 
nected with the progress of the trial, however unimportant it 
may appear. Record the time of every occurrence and the 
time of taking every weight and every observation. 

The coal should be weighed and delivered to the fireman 
in equal proportions, each sufficient for not more than one 
hour's run, and* a fresh portion should not be delivered until 
the previous one has all been fired. The time required to 
consume each portion should.be noted, the time being recorded 
at the instant of firing the last of each portion. It is desir- 
able that at the same time the amount of water fed into the 
boiler should be accurately noted and recorded, including the 
height of the water in the boiler, and the average pressure of 
steam and temperature of feed during the time. By thus 
recording the amount of water evaporated by successive por- 
tions of coal, the test may be divided into several periods if 
desired, and the degree of uniformity of combustion, evapo- 
ration, and economy analyzed for each period. In addition 
to these records of the coal and the feed- water, not less frequently 



BOILER TESTING 209 

than every half hour, observations should be made of the tem- 
perature of the feed-water, of the flue gases, of the external air of 
the boiler room, of the temperature of the furnace when a furnace 
pyrometer is used, also of the pressure of steam, and of the 
readings of the instruments for determining the moisture in the 
steam. A log should be kept on properly prepared blanks con- 
taining columns for record of the various observations. 

When the " standard method " of starting and, stopping the 
test is used, the hourly rate of combustion and of evaporation 
and the horse power should be computed from the records taken 
during the time when the fires are in active condition. This 
time is somewhat less than the actual time which elapses 
between the beginning and end of 'the run. The loss of 'time 
due to kindling the fire at the beginning and burning it out at 
the end makes this course necessary.. 

XIV. Quality of Steam. — The percentage of moisture in the 
steam should be determined by the use of either a throttling 
or a separating steam calorimeter. The sampling nozzle should 
be placed in the vertical steam pipe rising from the boiler. 
It should be made of one-half-inch pipe, and should extend 
across the diameter of the steam pipe to within half an inch 
of the opposite side, being closed at the end and perforated 
with not less than twenty one-eighth-inch holes equally distrib- 
uted along and around its cylindrical surface, but none of 
these holes should be nearer than one-half inch to the inner 
side of the steam pipe. The calorimeter and the pipe leading 
to it should be well covered with felting. Whenever the indica- 
tions of the throttling or separating calorimeter show that the 
percentage of moisture is irregular, or occasionally in excess of 
three per cent, the results should be checked by a steam 
separator placed in the steam pipe as close to the boiler as 
convenient, with a calorimeter in the steam pipe just beyond the 
outlet from the separator. The drip from the separator should 
be caught and weighed, and the percentage of moisture com- 
puted therefrom added to that shown by the calorimeter. 

Superheating should be determined by means of a ther- 
mometer placed in a mercury well inserted in the steam pipe. 
The degree of superheating should be taken as the difference 
between the reading of the thermometer for superheated steam 
and the readings of the same thermometer for saturated steam 



210 POWER PLANT TESTING 

at the same pressure as determined by a special experiment, 
and not by reference to steam tables. 

For calculations relating to quality of steam and corrections 
for quality of steam, see pages 46-60. 

XV. Sampling the Coal and Determining its Moisture. — As 
each barrow load or fresh portion of coal is taken from 
the coal pile, an average shovelful is selected from it and 
placed in a barrel or box in a cool place and kept until the 
end of the trial. The samples are then mixed and broken 
into pieces not exceeding 1 inch in diameter, and reduced 
by the process of repeated quartering and crushing until a 
final sample weighing about 5 pounds is obtained, and the size 
of the larger pieces is such that they will pass through a sieve 
with one-quarter-inch meshes. From this sample two one-quart 
air-tight glass preserving jars, or other air-tight vessels which 
will prevent the escape of moisture from the sample, are to 
be promptly filled, and these samples are to be kept for sub- 
sequent determinations of moisture and of heating value and 
for chemical analyses. During the process of quartering, when 
the sample has been reduced to about 100 pounds, a quarter 
to a half of it may be taken for an approximate deterrnination 
of moisture. This may be made by placing it in a shallow 
iron pan, not over 3 inches deep, carefully weighing it, 
and setting the pan in the hottest place that can be found 
on the brickwork of the boiler setting of flues, keeping it there 
for at least 12 hours, and then weighing it. The determination 
of moisture thus made is believed to be approximately accurate 
for anthracite and semi-bituminous coals, and also for Pitts- 
burg or Youghiogheny coal; but it cannot be relied upon for 
coals mined west of Pittsburg, or for other coals containing 
inherent moisture. For these latter coals it is important that 
a .more accurate method be adopted. The method recommended 
by the Committee for all accurate tests, whatever the character 
of the coal, is described as follows : 

Take one of the samples contained in the glass jars, and 
subject it to a thorough air-drying, by spreading it in a thin 
layer and exposing it for several hours to the atmosphere of a 
warm room, weighing it before and after, thereby determining 
the quantity of surface moisture it contains. Then crush the 
whole of it by running it through an ordinary coffee mill 



BOILER TESTING 211 

adjusted so as to produce somewhat coarse grains (less than one- 
sixteenth-inch), thoroughly mix the crushed sample, select from 
it a portion of from 10 to 50 grams, weigh it in a balance which 
will easily show a variation as small as 1 part in 1000, and 
dry it in an air or sand bath at a temperature between 240 
and 280 degrees Fahrenheit for one hour. Weigh it and record 
the loss, then heat and weigh it again repeatedly, at intervals 
of an hour or less ; until the minimum weight has been reached 
and the weight begins to increase by oxidation of a portion 
Of the coal. The difference between the original and the min- 
imum weight is taken as. the moisture in the air-dried, coal. 
This moisture test should preferably be made on duplicate 
samples, and the results should; agree within 0.3 to 0.4 of one 
per cent, the mean of the two determinations being taken as 
the correct result. The sum of the percentage of moisture thus 
found and the percentage of surface moisture previously deter- 
mined is the total moisture. 

XVI. Treatment of Ashes and Refuse. — The ashes and refuse 
are to be weighed in a dry state. If it is found desirable to 
show the principal characteristics of the ash, a sample should 
be subjected to a proximate analysis and the actual amount 
of incombustible material determined. For elaborate trials a 
complete analysis of the ash and refuse should be made. 

XVII. Calorific Tests and Analysis of Coal. — The quality 
of the fuel should be determined either by heat test or by 
analysis, or by both. 

The rational method of determining the total heat of com- 
bustion is to burn the sample of coal in an atmosphere of 
oxygen gas, the coal to be sampled as directed in Article XV. 
of this code. 

The chemical analysis of coal should be made only by an 
expert chemist. The total heat of combustion computed from 
the results of the ultimate analysis may be obtained by the 
use of Dulong's formula (with constants modified by recent 

determinations), viz., 1 4,6006" + 62,000 lH ] +4000S, in 

which C, H, O, and 5 refer to the proportions of carbon, 
hydrogen, oxygen, and sulphur respectively, as determined by 
the ultimate analysis. 1 

1 Favre and Silberman give 14,544 B.T.U. per pound carbon; Berthe- 



212 POWER PLANT TESTING 

It is desirable that a proximate analysis should be made, 
thereby determining the relative proportions of volatile matter 
and fixed carbon. These proportions furnish an indication of 
the leading characteristics of the fuel, and serve to fix the 
class to which it belongs. As an additional indication of the 
characteristics of the fuel, the specific gravity should be 
determined. 

XVIII. Analyses of Flue Gases. — The analysis of the flue 
gases is an especially valuable method of determining the 
relative value of different methods of firing, or of different 
kinds of furnaces. In making these analyses great care should 
be taken to procure average samples — since the composition 
is apt to vary at different points of the flue. 

The composition is also apt to vary from minute to minute, 
and for this reason the drawings of gas should last a consider- 
able period of time. Where complete determinations are 
desired, the analyses should be intrusted to an expert chemist. 
For approximate determinations " Orsat " * apparatus may be 
used by the engineer. 

For the continuous indication of the amount of carbonic 
acid present in the flue gases, an instrument may be employed 
which shows the weight of the sample of gas passing through it. 

XIX. Smoke Observations. — It is desirable to have a uni- 
form system of determining and recording the quantity of 
smoke produced where bituminous coal is used. The system 
commonly employed is to express the degree of smokiness 
by means of percentages dependent upon the judgment of 
the observer. The Committee does not place much value upon 
a percentage method, because it depends so largely upon the 
personal element, but if this method is used, it is desirable 
that, so far as possible, a definition be given in explicit terms, 
as to the basis and method employed in arriving at the per- 
centage. 

XX. Miscellaneous. — In tests for purposes of scientific 
research, in which the determination of all the variables 
entering into the test is desired, certain observations should 

lot 14,647 B.T.U. Favre and Silberman give 62,032 B.T.U. per pound 
hydrogen; Thomsen 61,816 B.T.U. 

1 See R. S. Hale's paper on " Flue Gas Analysis Transactions A.S.M.E., 
vol. 18., page 901. 



BOILER TESTING 213 

be made which are in general unnecessary for ordinary tests. 
These are the measurement of the air supply, the determina- 
tion of its contained moisture, the determination of the amount 
of heat lost by radiation, of the amount of infiltration of air 
through the setting, and (by condensation of all the steam 
made by the boiler) of the total heat imparted to the water. 

XXI. Calculations of Efficiency. — Two methods of defining 
and calculating the efficiency of a boiler are recommended. 
They are: 

„„ . , „ 1 ... Heat absorbed per lb. combustible 

i. Efficiency of the boiler = 7^—; — r^- — : ^ — r , : -rr-r ; 

Calorific value of 1 lb. combustible 

„,„ . r,i , -1 1 Heat absorbed per lb. coal 

2. Efficiency of the boiler and grate = ^n — =-f : —. — ^ — — , . 

Calorific value of 1 lb. coal 

The first of these is sometimes called the efficiency based 
on combustible, and the second efficiency based on coal. The 
first is recommended as a standard of comparison for all tests, 
and this is the one which is understood to be referred to when 
the word " efficiency " alone is used without qualification. 
The second, however, should be included in a report of a test, 
together with the first, whenever the object of the test is to 
determine the efficiency of the boiler and furnace together 
with the grate (or mechanical stoker), or to compare different 
furnaces, grates, fuels, or methods of firing. 

The heat absorbed per pound of combustible (or per pound 
coal) is to be calculated by multiplying the equivalent evap- 
oration from and at 212 degrees per pound combustible (or 
coal) by 965.7. 1 

XXII. The Heat Balance. — An approximate " heat balance," 
or statement of the distribution of the heating value of the 
coal among the several items of heat utilized and heat lost 
may be included in the report of a test when analyses of the 
fuel and of the chimney gases have been made. It should be 
reported in the following form : 

1 This value is the one given in the accepted steam tables in 1899 
when this code was published. According to the more recent deter- 
minations it should be 970. (See Marks and Davis' and Peabody's revised 
Steam Tables.) 



214 



POWER PLANT TESTING 



Heat Balance, or Distribution of the Heating Value of the 
Combustible. 

Total Heat Value of i lb. of Combustible B.T.U. 



Heat absorbed by the boiler = evaporation from 
and at 2 1 2 degrees per pound of combustible 

Xq-65-7- 1 

Loss due to moisture in coal = per cent, of moisture 
referred to combustible -^ioo><[(2i2— if) + 966 1 
+ o. 48 (T — 212) ](/ = temperature of air in the 
boiler-room, T =that of the flue gases). 

Loss due to moisture formed by the burning of hy- 
drogen = per cent, of hydrogen to combustible 
-4-100 X9X[2i 2 (-0 + 966 1 + 0.48(7-212)]. 

Loss due to heat carried away in the dry chimney 
gases = weight of gas per pound of combustible 

xo. 24 x(r-o. 

Loss due to incomplete combustion of carbon = 
CO per cent C in combustible 

C0 2 + CO 100 

Loss due to unconsumed hydrogen and hydrocar- 
bons, to heating the moisture in the air, to 
radiation, and unaccounted for. (Some of 
these losses may be separately itemized if data 
are obtained from which they may be calcu- 
lated). 

Totals 



1 This value is the one given in the accepted steam tables in 1899 when this code was 
published. According to the more recent determinations it should be 970. (See Marks 
and Davis' and Peabody's revised Steam Tables.) 

2 The weight of gas per pound of carbon burned may be calculated from the gas anal- 
yses as follows : 

, , iiC02 + 8 0+7(CO + N ) . ,. , ' „„ „ ,, r 

Dry gas per pound carbon = n ~ ,nn\ • m which CO2, CO, O and N are the 

3(,OU2 + OU,) 

percentages by volume of the several gases. As the sampling and analyses of the gases in 
the present state of the art are liable to considerable errors, the result of this calculation 
is usually only an approximate one. The heat balance itself is also only approximate for 
this reason, as well as for the fact that it is not possible to determine accurately the per- 
centage of unburned hydrogen or hydrocarbons in the flue gases. 

The weight of dry gas per pound of combustible is found by multiplying the dry gas 
per pound of carbon by the percentage of carbon in the combustible, and dividing by 100. 

3 CO2 and CO are respectively the percentage by volume of carbonic acid and carbonic 
oxide in the flue gases. The quantity 10, 150 = Number of heat units generated by burning 
to carbonic acid one pound of carbon contained in carbonic oxide. 




XXIII. Report of the Trial. — The data and results should 
be reported in the manner given in either one of the two fol- 
lowing tables, omitting lines where the tests have not been 
made as elaborately as provided for in such tables. Additional 



BOILER TESTING 215 

lines may be added for data relating to the specific object of 
the test. The extra lines should be classified under the headings 
provided in the tables, and numbered as per preceding line, 
with sub letters a, b, etc. The Short Form of Report, Table 
No. 2, is recommended for commercial tests and as a con- 
venient form of abridging the longer form for publication when 
saving of space is desirable. For elaborate trials, it is recom- 
mended that the full log of the trial be shown graphically, 
by means of a chart. (Fig. 179.) 

TABLE NO. 1. 

Data and Results of Evaporative Test. 

Arranged in accordance with the Complete Form advised by the Boiler 
Test Committee of the American Society of Mechanical Engineers. 
Code of 1899. 

Made by of boiler at to 

determine 

Principal conditions governing the trial 



Kind of fuel l 

Kind of furnace 

State of the weather 

Method of starting and stopping the test (" standard " or " alternate," 
Art. X. and XL, Code) 

1 . Date of trial 

2. Duration of trial hours. 

. .-.. Dimensions and Proportions. 

(A complete description of the boiler, and drawings of the same if of 
unusual type, should be given on an annexed sheet.) 

3. Grate surface width length area. . . . sq. ft. 

4. Height of furnace ins. 

5. Approximate width of air spaces in grate in. 

6. Proportion of air space to whole grate surface per cent. 

7. Water-heating surface sq. ft. 

8. Superheating surface 

9. Ratio of water-heating surface to grate surface — to 1. 

10. Ratio of minimum draft area to grate surface 1 to — . 

Average Pressures. 
n. Steam pressure by gage lbs. per sq. in. 

12. Force of draft between damper and boiler ins. of water 

13. Force of draft in furnace 

14. Force. of draft or blast in ash pit 

I The items printed in italics correspond to the items in the "Short Form of Code " 



216 



POWER PLANT TESTING 



Average Temperatures. 

15. Of external air deg. 

16. Of fireroom 

17. Of steam 

18. Of feed water entering heater 

19. Of feed water entering economizer 

20. Of feed water entering boiler 

2 1 . Of escaping gases from boiler 

22. Of escaping gases from economizer 



Fuel. 

23. Size and condition 

24. Weight of wood used in lighting fire. . . 
2 5 . Weight of coal as fired x 

26. Percentage of moisture in coal 2 

27. Total weight of dry coal consumed 

28. Total ash and refoise 

29. Quality of ash and refuse 

30. Total combustible consumed. . 

3 1 . Percentage of ash and refuse in dry coal . 



lbs. 

per cent, 
lbs. 



, lbs. 
per cent. 



Proximate Analysis of Coal. 

Of Coal. 
32". Fixed carbon per cent. 

33. Volatile matter 

34. Moisture 

35- Ash 



Of Combustible 
. . . .per cent. 



36. Sulphur, separately determined 



r 00 per cent. 1 00 per cent. 



Ultimate Analysis of Dry Coal. 
(Art. XVII., Code.) 

Of Coal. 



Of Combustible. 



37. Carbon (C) 

38. Hydrogen (H) . 

39. Oxygen (O) . . . 

40. Nitrogen (N) . . 

41. Sulphur (S) . . . 

42. Ash 



per cent per c 



100 per cent 100 per cent. 
43. Moisture in sample of coal as received. . . 

1 Including equivalent of wood used in lighting the fire, not including unburnt coal 
withdrawn from furnace at times of cleaning and at end of test. One pound of wood is 
taken to be equal to 04 pound of coal, or, in case greater accuracy is desired, as having a 
heat value equivalent to evaporation of 6 pounds of water from and at 212 degrees per 
pound. (6X965 7 = 5794 B T.U ) The term "as fired" means in its'actual condition, 
including moisture. 

8 This is the total moisture in the coal as found by drying it artificially, as described in 
Art. XV. of Code. 



BOILER TESTING 



217 



Analysis of Ash and Refuse. 

44. Carbon 

4.5. Earthy matter 

Fuel per Hour. 

46. Dry coal consumed per hour 

47. Combustible consumed per hour 

48. Dry coal per square foot of grate surface per hour 

49. Combustible per square foot of water-heating surface 

per hour 



per cent. 



lbs. 



Calorific Value of Fuel. 
(Art. XVII., Code.) 

50. Calorific value by oxygen calorimeter, per lb. of dry coal 

51. Calorific value by oxygen calorimeter, per lb. of combus- 



B.T.U. 



52. Calorific value by analysis, per lb. of dry coal ' 

53. Calorific value by analysis, per lb. of combustible.. 



Quality of Steam. 

54. Percentage of moisture in steam 

55. Number of degrees of superheating 

56. Quality of steam (dry steam = unity") . 



per cent- 
deg. 



Water. 

Total weight of water fed to boiler 2 

Equivalent water fed to boiler from and at 2 1 2 degrees 
Water actually evaporated, corrected for quality of steam 

Factor of evaporation 3 

Equivalent water evaporated into dry steam from and 
at 212 degrees 4 (Item 59 Xltem 60) 



lbs. 



Water per Hour. 

62. Water evaporated per hour, corrected for quality of steam 

63 . Equivalent evaporation per hour from and at 2 1 2 degrees 2 

64. Equivalent evaporation per hour from and at 212 

per square foot of water-heating surface 2 



1 See formula for calorific value under Article XVII. of Code. 

2 Corrected for inequality of water level and of steam pressure at beginning and end 
of test. 

3 Factor of evaporation = — — , in which H and 4 are respectively the total heat in 

965.7 
steam of the average observed pressure, and in water of the average observed temperature 
of the feed. According to the newer steam tables the divisor in this fraction should be 970. 
* The symbol " U. E." meaning " Units of Evaporation," may be conveniently sub- 
stituted for the expression " Equivalent water evaporated into dry steam from and at 212 
degrees." its definition being given in a footnote. 



218 



POWER PLANT TESTING 
Horse Power. 



65. Horse power developed. (34 J lbs. of water evaporated 

per hour into dry steam from and at 2 1 2 degrees, equals 

011c horse power) l H. P. 

66. Builder's rated horse power 

67. Percentage of builders' rated horse power developed. . . . per cent. 



Economic Results. 

68. Water apparently evaporated under actual conditions 

per pound of coal as fired. {Item 57 -j- Item 25) . . 

69. Equivalent evaporation from and at 212 degrees per 

pound of coal as fired. 2 (Item 61 -hltem 25.) 

70. Equivalent evaporation from and at 212 degrees per 

pound of dry coal. 2 (Item 61 -hltem 27.) 

71. Equivalent evaporation from and at 212 degrees per 

pound of combustible. 2 (Item 61 -s- Item 30.) 

(If the equivalent evaporation, Items 69, 70, and 71, 
is not corrected for the quality of steam, the fact 
should be stated.) 



lbs. 



Efficiency. 
(Art. XXL, Code.) 

72. Efficiency of the boiler; heat absorbed by the boiler per 

lb. of combustible divided by the heat value of one lb. 
of combustible 2 

73. Efficiency of boiler, including the grate; heat absorbed 

by the boiler, per lb. of dry coal, divided by the heat 
value or one lb. of dry coal 



per cent. 



Cost of Evaporation. 

74. Cost of coal per ton of lbs. delivered in ooiler room $ 

75. Cost of fuel for evaporating 1,000 lbs. of water under 

observed conditions $ 

76. Cost of fuel used for evaporating 1,000 Ibs^ of water from 

and at 2 1 2 degrees $ 

Smoke Observations. 

77. Percentage of smoke as observed . per cent. 

78. Weight of soot per hour obtained from smoke meter. ounce. 

79. Volume of soot per hour obtained from smoke'meter cu. in. 



1 Held to be the equivalent of 30 lbs. of water per hour evaporated from 100 degrees 
Fahrenheit into dry steam at 70 lbs. gage pressure. (See Introduction to Code, page 201.) 

2 In all cases where the word combustible is used, it means the coal without moisture 
and ash, but including all other constituents. It is the same as what is called in Europe 
" coal dry and free from ash." 



BOILER TESTING 



219 



Methods of Firing. 

80. Kind of firing (spreading, alternate, or coking) 

81. Average thickness of fire 

82. Average intervals between firings for each furnace 

during time when fires are in normal condition 

83 . Average interval between times of leveling or break- 

ing up 

Analyses of the Dry Gases. 

84. Carbon dioxide (C0 2 ) 

85. Oxygen (O) 

86. Carbon monoxide (CO) 

8 7 . Hydrogen and hydrocarbons 

88. Nitrogen (by difference) (N) 



per cent. 



:oo per cent. 



TABLE NO. 2. 

Data and Results of Evaporative Test. 

Arranged in accordance with the Short Form advised by the Boiler Test 
Committee of the American Society of Mechanical Engineers. Code 
of 1899. 

Made by on .... -. boiler, at to 

determine 

Kind of fuel 

Kind of furnace 

Method of starting and stopping the test (" standard " or " alternate," 

Art. X. and XL, Code) 

Grate surface sq. ft. 

Waterheating surface 

Superheating surface " . 



Total Quantities. 

1 . Date of trial 

2 . Duration of trial 

3. Weight of coal as fired x 

4. Percentage of moisture in coal ' 

5. Total weight of dry coal consumed 

6. Total ash and refuse 

7 . Percentage of ash and refuse in dry coal 

8. Total weight of water fed to the boiler ' 

9. Water actually evaporated, corrected for moisture or 

superheat in steam 

10. Equivalent water evaporated into dry steam from and 
at 2 1 2 degrees 1 

i See footnotes of Complete Form, pages 216 ancj 217. 



hours. 

lbs. 
per cent. 

lbs. 

per cent, 
lbs. 



220 POWER PLANT TESTING 

Hourly Quantities. 

ii. Dry coal consumed per hour . lbs. 

12. Dry coal per square foot of grate surface per hour. . . 

13. Water evaporated per hour corrected for quality of 

steam 

14. Equivalent evaporation per hour from and at 212 

degrees l 

15. Equivalent evaporation per hour from and at 212 

degrees per square foot of water-heating surface l . 

Average Pressures, Temperatures, etc. 

16. Steam pressure by gage lbs. per sq. in. 

1 7 . Temperature of feed water entering boiler deg. 

Temperature of escaping gases from boiler 

Force of draft between damper and boiler ins. of water. 

Percentage of moisture in steam, or number of degrees 

of superheating , per cent, or deg. 

Horse Power. 

21. Horse power developed (Item 14-^34^) ' H. P. 

22. Builder's rated horse power 

23. Percentage of builder's rated horse power developed. per cent. 

Economic Results. 

24. Water apparently evaporated under actual conditions 

per pound of coal as fired. (Item 8 h- Item 3) lbs. 

25. Equivalent evaporation from and at 212 degrees per 

pound of coal as fired. 1 (Item 10 -h Item 3) 

26. Equivalent evaporation from and at 212 degrees per 

pound of dry coal. 1 (Item 10 -j- Item 5) 

27. Equivalent evaporation from and at 212 degrees per 

pound of combustible. 1 [Item 10-^ (Item 5— Item 

6)] •• 

(If Items 25, 26, and 27 are not corrected for quality 
of steam, the fact should be stated.) 

Efficiency. 

28. Calorific value of the dry coal per pound B.T.U. 

29. Calorific value of the combustible per pound 

30. Efficiency of boiler (based on combustible) 1 per cent. 

31. Efficiency of boiler, including grate (based on dry coal) 

Cost of Evaporation. 

3 2 . Cost of coal per ton of lbs delivered in boiler room $ 

^2- Cost of coal required for evaporating 1000 pounds of 

water from and at 2 1 2 degrees $ 

1 See footnotes of Complete Form, pages 217 and 218. 



BOILER TESTING 221 



EFFICIENCY OF THE BOILER 



The efficiency of the boiler, including the grate, or the 
efficiency based on coal, is the quotient arising from dividing 
heat absorbed by the boiler by the heating value of the total 
amount of coal supplied to the boiler, including the coal which 
falls- through the grate. It may be conveniently calculated 
by multiplying the number of pounds of water evaporated 
from and at 212 degrees Fahrenheit into dry steam per pound 
of dry coal by 965.7, 1 and dividing the product by the heating 
value in B. T. U. of one pound of dry coal. 

The efficiency of -the boiler, not including the grate, or 
the efficiency based on combustible, is the quotient arising 
from dividing the heat absorbed by the boiler by the heating 
value of the combustible burned. It may be calculated by 
multiplying the number of pounds of water evaporated from 
and at 212 degrees Fahrenheit into dry steam per pound of 
combustible by 965. 7, 1 - and dividing the product by the 
heating value in B. T. U. of one pound of combustible; 
the term " combustible " being defined as coal dry and free 
from ash, or the coal supplied to the boiler less its moisture 
and the ash and unburn ed coal which falls through the grate 
or is otherwise withdrawn from the furnace. 

The efficiency of the boiler, not including the grate (or the 
efficiency based upon combustible) is a more accurate measure 
of comparison of different boilers than the efficiency including 
the grate (or the efficiency based upon coal), for the latter is 
subject to a number of variable conditions, such as size and 
character of the coal, air-spaces between the grate bars, skill 
of the fireman in saving coal from falling through the grate, 
etc. It is, moreover, subject to errors of sampling the coal 
for drying and for analysis, which affect the result to a greater 
degree than they do the efficiency based upon combustible, 
for the reason that the heating value per pound of com- 
bustible of any sample selected from a given lot (such as a car- 
load) of coal is practically a constant quantity and is inde- 
pendent of the percentage of moisture and ash in the sample; 
while the sample itself, upon the heating value of which the 
efficiency based on coal is calculated, may differ in its per- 
*See page 201 and footnote, page 213. 



222 POWER PLANT TESTING 

centage of moisture and ash from the average coal used in 
the boiler test. 

When the object of a boiler test is to determine its efficiency 
as an absorber of heat, or to compare it with other boilers, 
the efficiency based on combustible is the one which should 
be used; but when the object of the test is to determine the 
efficiency of the combination of the boiler, the furnace, and 
the grate, the efficiency based on coal must necessarily be 
used. 

It has been proposed that in reporting the efficiency of a 
boiler when the fuel used contains hydrogen, the efficiency 
should be considered to be the sum of the percentage of the 
heating value of the fuel which is utilized by the boiler in 
making steam of the percentage of that heating value which is 
lost in the shape of latent heat in the moisture in the chimney 
gases, which moisture is formed by the burning of the hydrogen. 
This latent heat may amount to over three per cent of the total 
heating value of the fuel. The reason assigned for this pro- 
posal is that, since it is impossible for this heat to be utilized by 
the boiler because the gases are discharged at a temperature 
above 212 degrees Fahrenheit, it should not be charged against 
the boiler. It is not considered advisable that this method 
of reporting the efficiency should be adopted (1) because 
it is opposed to the generally accepted definition of effi- 
ciency, which is the useful work received from an apparatus 
divided by the work (or heat value of the fuel) put into it; 

(2) because in order to calculate it, it is necessary to know 
both the percentage of hydrogen in the coal and whether or 
not all of this hydrogen has been burned to H 2 0, the first 
requiring an analysis of the coal, which is not always obtainable, 
and the second an analysis of the gases for hydrogen, which 
cannot be obtained with any approximation to accuracy with 
our present methods of sampling and analyzing gases; and 

(3) because it is opposed to the almost universal custom of 
reporting boiler tests. It is true that the latent heat of the 
water in the chimney gases cannot be utilized (unless an econ- 
omizer which discharges its gases below 212 degrees is used), 
and it is not the fault of the boiler that it cannot be utilized. 
It may be considered the misfortune of the boiler, when tested 
with hydrogenous coal, similar to the misfortune under which 



BOILER TESTING 223 

an engine labors when it is tested while supplied with a con- 
denser which gives a vacuum of less than 30 inches of mercury. 
The engine might give a higher efficiency with a vacuum of 
30 inches than it would with one of 27 or 28 inches; but it 
is not customary to credit the engine with the efficiency which 
it loses on account of the imperfect vacuum. 

Since it is well understood that a boiler cannot show quite 
as high an efficiency (as commonly defined) when using bitu- 
minous coal high in hydrogen as when using anthracite nearly 
free from hydrogen, no harm is done, and much confusion is 
avoided, by reporting the efficiency as the. percentage of the 
heating value of the coal which is actually utilized in making 
steam. The fact that bituminous coal is used is always stated 
in the report of a test made with that coal. If desired, a state- 
ment may also be made in the " heat balance " of the approxi- 
mate or estimated percentage of heat which is lost in the 
latent heat of the moisture in the chimney gases, together with 
the loss- due to moisture in the coal. 

DISTRIBUTION OF THE HEATING VALUE OF THE FUEL 

In the operation of a steam boiler the following distribu- 
tion of the total heating value of the fuel takes place : 

1 . Loss of coal or coke through the grate. 

2. Unburned coal or coke carried in the shape of dust or 
sparks beyond the bridge wall. 

3. Heating to 212 degrees the moisture in the coal, evap- 
orating it at that temperature, and evaporating the steam 
made from it to the temperature of the flue gases ^weight of 
the moisture in pounds X [(212 degrees — /) +966 1 +0.48(7"— 212)], 
in which T is the temperature (Fahrenheit) of the flue gases 
and t the temperature of the external air. 

4. Loss of heat due to steam which is formed by burning 
the hydrogen contained in the coal, and which passes into 
the chimney as superheated steam =9 times the weight of the 
hydrogen x[ (21 2— /) +966 1 +0.48(7— 212)]. 

5. Superheating the moisture in the air supplied to the 
furnace to the temperature of the flue gases ^weight of the 
moisture X 0.48(7"—/). 

'See footnote, page 213. 



224 POWER PLANT TESTING 

6. Heating of the gaseous products of combustion (not 
including steam) to the temperature of the flue =their weight 

xo.2 4 (r-o. 

7. Loss due to imperfect burning of the carbon of the coal 
and to non-burning of the volatile gases. 

8. Radiation from the boiler and furnace. 

9. Heat absorbed by the boiler, or useful work. 

Item 1 depends upon the size of the spaces between the 
grate bars; upon the kind of grate, as a plain, shaking, or 
traveling grate; upon the size of the coal; upon the char- 
acter of the coal, as it requires to be more or less distributed 
on the grate in order to get a sufficient supply of air through 
it; upon the rate of driving of the furnace, rapid driving with 
some coals requiring more frequent shaking or cleaning of the 
grate than slow driving ; and upon the skill of the fireman. 

Item 2 depends upon the nature and fineness of the coal 
and tipon the force of the draft. It is usually so small as to 
be inappreciable in its effects upon the results of the trial of 
a stationary boiler driven with natural draft, but in locomo- 
tives, with rapid rates of combustion, it often becomes quite 
important. 

Item 3 depends upon the amount of moisture in the coal. 

Item 4 depends upon the amount of hydrogen in the coal. 

Item 5 depends upon the amount of moisture in the air. 
The moisture in the air may be obtained from its temperature 
and relative humidity, as determined by a wet-and-dry bulb 
thermometer by reference to hygrometric tables. The loss of 
heat due to the moisture in the air will rarely exceed 0.25 
per cent, of the heating value of the fuel, and it may usually, 
therefore, be neglected. (For hygrometric tables see page 403.) 

Item 6 depends chiefly upon the type and proportions of 
the boiler, and upon the rate at which it is driven. This 
item is usually the largest of all the heat losses. 

Items 3, 4, 5, and 6 depend also on the temperature of 
the flue gases. 

Item 7 depends upon the character of the coal and of the 
furnace, and upon the skill of the fireman. This loss may 
be very large, 20 per cent or more of the heating value of the 
coal, when highly bituminous coals are used in a furnace not 
adapted to them. 



BOILER TESTING 225 

Item 8 depends chiefly upon the type, size, and setting 
of the boiler, and, when expressed as a percentage of the total 
heat of the fuel, upon the rate at which it is driven. 

Item 9 is the heat absorbed by the boiler, or the useful 
work. It is also the difference between the total heating value 
of the coal and of the sum of the losses of items i to 8 inclusive. 



COMPUTATION OF THE WEIGHT OF THE CHIMNEY GASES FROM 
THE ANALYSIS BY VOLUME OF THE DRY GAS. 

Two methods of calculating from the analysis by volume 
of the dry chimney gases the number of pounds of dry chimney 
gases per pound of carbon, or the weight of air supplied per 
pound of carbon, have been given by different writers. These 
may be expressed in the shape of formula? as follows : 

,., „ A A An nC0 2 + 80 + 7(CO + N) „, 

(A) Pounds dry gas per pound C = /y '- (6i) 

3(uu 2 + uuj 

, D , D , . An _"(C0 2 + 0)+CO 

(B) Pounds air per pound C = 5-8— — ^r ^ . . (62) 

Formula A may be derived from the method of computation 
given in Mr. R. S. Hale's paper on " Flue-Gas Analyses," 
Transactions American Society of Mechanical Engineers, vol. 
18, page 902, and formula B from the method given in Peabody's 
and Miller's " Treatise on Steam Boilers." Both are based on 
the principle that the density, relatively to hydrogen, of an 
elementary gas (O and N) is proportional to its atomic weight, 
and that of a compound gas (CO and C0 2 ) to one-half its 
molecular weight. Both formulas are very nearly accurate when 
pure carbon is the fuel burned, but formula B is inaccurate 
when the fuel contains hydrogen, for the reason that that 
portion of the oxygen of the air supply which is required to 
burn the hydrogen is contained in the chimney gas as H 2 0, and 
does not appear in the analysis of the dry gas. 

The following calculations of a supposed case of combustion 
of hydrogenous fuel illustrates the accuracy of formula A and 
the inaccuracy of formula B. Assume that the coal has the 



226 



POWER PLANT TESTING 



following analysis: C, 66.50; H, 4.55; O, 8.40; N, 1.00; water, 
10.00; ash and sulphur, 9.55 — total, 100. Assume also that 
one-tenth of the C is burned to CO, and nine-tenths to C0 2 ; 
that the air supply is 20 per cent in excess of that required 
for this combustion; that the air contains 1 per cent by 
weight of moisture ; and that the S in the coal may be considered 
as part of the ash. We then have the following synthesis of 
results of the combustion of 100 pounds of coal: 





O from 
Air 


N = 
ox 15 


Total Air 


C0 2 


CO 


H02 


59.85 lbs. C to C0 2 X2f 
6.65 " CtoCO Xi| 
3.50 " HtoH,OX8 


T59.60 

8.87 

28 .OO 


534-3 1 
29.70 
93-74 


693.91 

38.57 
121.74 


219.45 






15-52 


31-5° 








196.47 


657-75 


854.22 




1.05 " HtoH 2 0\ 
8.40 " HtoHjO/ 






9-45 












1. 00 " N 




1 .00 










9.55 ' Ash and S 


























Excess of air 20 per cent. 


39-29 


i3i-55 


170.84 
















1025.06 




Moisture in air 1 per cent. 










10.25 












Total wt. gases, 11 2 5. 67 lbs. = 
Total dry gases, 1064.56 lbs. 

Per Cent. 
Total dry gases, by weight, 
Total dry gases, by volume, 


39-29 


3-69 
3-5o8 


790.30 

N 
74.24 
80.656 




219.45 

CO2 

20 . 61 
14.252 


15-52 

CO 

1-546 
1-584 


61 . 20 



Total gases 1 125.76 + ash and S 9.55 = 1135.3 1 lbs. total products. 
Total air 102 5.06 + moisture in air 10.25 + coal 100 = 1135.31 lbs. 
Dry gas per lb. coal 10.6456; per lb. carbon = 10.6456 -h .665 =16.008 lbs. 
Dry air per lb. coal 10.2506; per lb. carbon = 10.2506 -^.665 = 15.414^3. 

Computation of the weight of dry gas and of air per lb. carbon. 

Formula A: 



Dry gas per lb. C 
Formula B : 



.252X11+3.508X8 + 82.240X7 
3(14.252 + 1.584) 



= 16.008. pounds. 



.. . An 2(14- 252+3. 5o8) + i584 

Air per pound L = 5.8 — = 13.589 pounds. 

14. 252 + 1. 584 

The error in the last result is 15.414 — 13-589 = 1.825 pounds. 



BOILER TESTING 



227 




228 POWER PLANT TESTING 

Professor D. S. Jacobus gives another formula for the air 
per pound of carbon, in which the error of formula 62 is almost 
entirely avoided. It is 

Formula C: 

7N N 

Air per pound C= 3(C02 + CO) ^o. 77) or O , 33(c o 2+C0) , (63) 

in which N, C0 2 , and CO are the percentages by volume of 
these gases. Making the computation from the data of the 
above analysis, we have: 

80.656 

Air per pound C = ^ —— = 15.434 pounds, 

P F 0.33(14.252+1.584) .^** 

the true value being 15.414 pounds. 

Fig. 180 is a diagram showing the heat distribution and 
losses in a steam boiler and engine plant, due mainly to Parsons. 
The method of showing graphically the percentage of losses is 
particularly interesting. 



CHAPTER XI 

STEAM ENGINE TESTING 

Most important of the tests made of nearly all classes of 
machinery is that for mechanical efficiency; meaning the 
comparison of the useful work performed with the amount 
of work theoretically possible to obtain with a perfect machine. 
In other words, in an engine the mechanical efficiency, E m , 
is the ratio of the brake horse power to the indicated horse 
power, or 

■p TT p 

Em= L ' H 'p' ($4) ■ 

The difference between the indicated horse power and the 
brake horse power is called the friction horse power. In many 
cases with very large engines, it is not readily possible to 
obtain the brake horse power directly, and in such cases it 
is customary to obtain approximately the horse power lost 
in friction from a so-called " friction indicator diagram," 
obtained from the areas of indicator diagrams when the only 
work done is that required to overcome its own friction, or in 
common parlance, when the engine is " running light." The 
brake horse power is then taken to be the difference between 
the indicated horse power and the friction horse power. Such 
a determination of friction horse power and of mechanical 
efficiency by calculation cannot be considered very accurate, 
because the friction of an engine increases slightly with in- 
creasing loads. 

Observed and calculated data of mechanical efficiency may 
be tabulated in the following form : 

229 



230 



POWER PLANT TESTING 



STEAM ENGINE TESTING 
TESTS FOR MECHANICAL EFFICIENCY AND FRICTION 



Date 

Description of engine tested 



Test made by . 



Tare of Brake lbs. Length of brake arm feet . 

Engine and Brake Constants (see pages 121 and 123.) 



No. of 
Read- 


Time. 


Weight on 
Brake.lbs. 




Areas of 

Indicator 

Cards, sq.ins. 


Indicated 
Horse power. 


Brake 
Horse 
power. 


Fric- 
tion 
Horse 
power. 


Mech. 
Effic. 


ing. 





■z, 


Head 

End. 


Crank 

End. 


Head. 

End. 


Crank 
End. 


Total 


% 





























Valve Setting (Slide Valve Engines). In order that steam 
may be used economically in an engine, it is necessary that 
the valve be set carefully and accurately, so that when an 
indicator card is taken the diagram obtained will be as nearly as 
possible like the ideal. Adjustment of a slide valve on an engine 
is accomplished in two different ways, with different effects : 

(1) By moving the valve on its stem; 

(2) By adjusting the eccentric. » 

To Set the Valve for Equal Leads. The valve should be 
placed first in such a position on its stem (valve rod) that 
the amount of its travel will be the same on the two sides 
of its mid-position. In other words, the valve is to be set on its 
stem so that its movement will be symmetrical with respect to 
the ports. Typical slide valves are shown in mid-position in 
Figs. 181 and 182. Setting the valve symmetrically or in mid- 
position is easily accomplished by turning the engine (or by 
moving the eccentric on the shaft) until the valve is brought 
to the farthest point of its travel on one side of its mid-position. 
Then measure the width 1 of the part of the steam port 'which 
is uncovered. The valve should then be shifted to the limit 
of its travel at the other end so that the width of the uncovered 

1 It is assumed of course that corresponding dimensions of the ports 
are the same at the two ends of the valve seat. 



STEAM ENGINE TESTING 



231 



portion of the steam port can be measured at that end. If 
the widths measured at the two ends are not the same, the 
valve must be moved on its stem a distance equal to half the 
difference between the widths of the uncovered ports. This 
movement of the valve will be in a direction away from the 



Exhaust Lap _J L_ 



-*| («- Exhaust Lap 



Steam Lap 




Ordinary D-slide Valve in Mid-position. 



port having the smaller opening. Measurements should be 
repeated and if the widths of the uncovered ports are still 
unequal this method of adjustment must be continued. 

By the method described the two leads of the valve will 
have been made the same; in other words, the distance the 



Exhaust Lap 



Steam Lap steam. Lap 



j**i Exhaust Lap 




Fig. 182. — Piston Type of Slide Valve in Mid-position. 

valve uncovers the steam ports when the engine is on the dead- 
centers will be the same at both ends of the cylinder. Now 
move the engine accurately to the dead-center * toward the 

1 An engine can be put on dead-center quite accurately by the " method 
of trammels." When the engine is just a little off the center to be deter- 
mined, make small scratch-marks opposite each other both on the cross- 
head and on one of the guides. Now set a pair of dividers or trammels with 
one end resting on the bedplate of the engine, its foundation, or some 
convenient stationary object near the fly-wheel, and with the other end 



232 POWER PLANT TESTING 

head end, for example, and move the eccentric on the shaft 
in the direction in which the engine is to run 1 until the 
steam port at the head end of the cylinder has been opened 
a distance equal to the lead required and in the position 
defined in general by stating that a further movement of the 
valve in the same direction will open the port wider. In this 
position the eccentric should be firmly fixed to the shaft. 
The engine should then be turned over to the other dead-center 
so that the lead can be measured at that end. If the leads are 
not the same, the difference should be halved, one part to 
be taken up by moving the valve on its stem, and the other 
by moving the eccentric. 

To set the valve for equal cut-offs, the valve is first set 
on its stem so that the travel will be the same on both sides 
of the mid-position as explained at the bottom of page 230 
to make its movement symmetrical with the ports. Now an 
adjustment of the eccentric must be made so that steam will 
be cut off at each end of the cylinder when the piston has moved 
the same distances or the same per cent of the stroke from 
the two ends. To perform this adjustment, mark on the 
cross-head as accurately as possible the limits of the stroke, 
and set the cross-head at the per cent of the stroke for cut-off 
appearing to be most suitable for the conditions of load. Move 
the eccentric on the shaft in the direction in which the engine 
is to run until it can be seen that the valve would be just 
closing the steam port at the end of the cylinder from which 
the piston is moving. Fasten the eccentric securely in this 
position and turn the engine over to observe whether the 
valve will be just closing the other steam port when the piston 
has moved the same distance, measured on the cross-head, 

mark a point on the fly-wheel. The engine should then be moved over 
or beyond the dead-center until the marks made on the cross-head and 
on the guide come together again. With the dividers set with the points 
the same distance apart as before again put a mark on the fly-wheel. 
Then if the engine is turned back so that the end of the dividers used to 
mark on the fly-wheel is at a point half way between the two marks, 
it will be set quite accurately on the dead-center required. In all these 
adjustments care must be taken to turn the engine each time in the 
same direction with respect to the dead-center so that the lost motion 
or back lash is taken up in the same direction. 

1 This applies only to a valve like the one in Fig. 181, which takes 
steam on the "outside." When the valve takes steam on the inside 
(Fig. 182) the eccentric must be moved in the opposite direction. 



STEAM ENGINE TESTING 233 

from the other end of the cylinder. If the setting is not 
correct, the error should be halved, correcting for one half by 
moving the valve on the stem and for the other by moving 
the eccentric on the shaft. This operation, which is a " cut 
and try " process, must be repeated until the required setting 
is secured. 

Methods similar to those described are preferred usually 
for the accurate setting of the slide valves of slow- and medium.- 
speed engines. High-speed engines as well as slow-speed 
engines of the Corliss type have their valves set usually on 
the basis of the information secured from indicator diagrams 
taken on the engines, showing approximately the " timing " 
of the events of the stroke. To set a slide valve successfully 



Cut Off 




Compression 



Atmospheric Line 
Fig. 183. — Indicator Diagram Illustrating the Point of Cut-off. 

by the " indicator " method, the valve and ports should be 
measured to determine the " lap " dimensions and port openings 
indicated in • Fig. 181, page 231, and the valve travel by 
direct measurements. "With these data a Zeuner 1 valve 
diagram should be constructed, showing a good steam dis- 
tribution for assumed lead or cut-off. Then construct the 
theoretical indicator card from the Zeuner diagram and adjust 
the setting of the valve on t*he stem and the eccentric on the 
shaft till a close approximation to the theoretical card is 
obtained. In this adjustment the first thing to be done is 
to equalize the valve travel by locating it on its stem so that 
the travel will be the same on both sides of its mid-position. 

1 It is beyond the scope of this book to take up a discussion of valve 
diagrams. The theory and construction of the Zeuner diagram is given 
in nearly all books on the steam engine. 



234 POWER PLANT TESTING 

Use a spring light enough to give an indicator diagram 
about 1 1 inches high so that events of the stroke, — admission, 
cut-off, release, and compression, will be shown as clearly as 
possible. Sometimes it is difficult to determine these events 
on a diagram on account of the curves gradually running into 
each other without the point separating the different curves 
being clearly defined. A good method for such cases is to 
produce along their regular trend both of the curves of which 
the intersection is required and take for the intersection the 
point where these curves cross each other. The method is 
illustrated on an indicator card in Fig. 183 showing the point 
of cut-off. 

In a slide valve engine it is not possible to set the valve 
to secure at the same time equal cut-offs and equal leads. 

Ideal and imperfect indicator diagrams taken from slide 
valve and Corliss engines are shown in Fig. 184. A little 
study of such diagrams may help to solve many difficulties in 
valve setting. 

Setting Corliss Valves. A brief desciiption 1 of the essential 
parts of the valve gear of a Corliss engine will assist in obtain- 
ing a clearer conception of the subject. In Figs. 185 and 
186 similar capital letters of reference indicate the same parts 
of the mechanism. 

Fig. 185 shows all the essential parts of the valve gear. 
The steam valves work in the chambers S, S and the exhaust 
valves work in the chambers E, E. The double-armed levers 
AC, AC, work loosely on the hubs of the valve-stem brackets 
and the lever arms B, B; the former are connected to the 
wrist plate W by the rods M, M ; the levers B, B are keyed to 
the valve stems V, V, and are also connected by the rods 0, 
to the dashpots D, D. The double-armed levers carry at their 
outer ends, C, C hardened steel catch plates, which engage 
with arms B, B, making the two arms B and C work in 
unison until steam is to be cut off; at this point another set 
of levers H, H, connected by the cam rods G, G to the governor, 
come into play, causing the catch plates to release the arms 
B, B, the outer ends of which are then pulled downward by 
the weight of the dashpot plunger, causing the steam valves 

1 This description is from American Machinist, vol. 18, page 391. 
For clearness the article is considered unusually good. 



STEAM ENGINE TESTING 



235 




236 



POWER PLANT TESTING 



to rotate on their axes and thus cut off steam. These are 
the essential features of the Corliss gear, although the design 
of the mechanism is greatly modified by different builders. 

The exhaust valve arms F are connected to the wrist plate 
by the rods N, N, and it is seen that all the valves receive 
their motion from the wrist plate; the latter receives its 
motion from the hook rod I; this rod is generally attached to 
a rocker arm, not shown; to this arm the eccentric rod is 




Corliss Valve Gear. 



also attached. The carrier arm is usually placed about mid- 
way between the wrist plate and eccentric, and in the center 
of its travel stands in a vertical position. 

The setting of the valves is not a difficult matter when, 
on the wrist plate, its support, valves and cylinder, the cus- 
tomary marks have been placed for finding the relative positions 
of wrist plate and valves. 

Now referring to Fig. 186, when the back bonnets of the 
valve chambers have been taken off, there will be found a 
mark or line a on the end of each steam valve s, s, coinciding 



STEAM ENGINE TESTING 



237 



with the working or opening edges of each valve ; another line b 
will be found on each face of the steam valve chamber coin- 
ciding with the working edge of the valve, and the line h, on 
the face of each exhaust valve chamber, coincides with the 
working edge of the exhaust port. On the hub of the wrist 
plate will be found a line d, coinciding with the center line 
d, k; lastly, there are three lines f, c, f, on the hub of the wrist- 
plate support, placed in such a way that when the line d 
coincides with the line c, the wrist plate will stand exactly 
in the center of its motion, and when the line d coincides with 
either of the lines f, f, the wrist plate will be at one of the 
extreme ends u or v of its travel. It should be noticed that 
since the lines f , e, f are drawn on the periphery of the hub of 




Fig. i 86. — Diagram of a Corliss Valve Mechanism 



the wrist-plate support, and the line d is drawn on the periph- 
ery of the wrist-plate hub, these lines cannot stand in a vertical 
line, as shown; we have adopted this way of showing them, 
simply for the purpose of making the matter plain. 

In setting the valves, the first step will be to set the wrist 
plate in its central position, so that lines c and d will coincide, 
and fasten the wrist plate in this position by placing a piece 
of paper between it and the washer L on its supporting pin. 
Now set the steam valves so that they will have a slight 
amount of lap, that is to say, the lines a, a must have moved 
a little beyond the lines b, b; the amount of this lap depends 
much on individual preference and experience; it ranges 
from ^ to -J inch for small engines, and from | to ^ inch for 
comparatively large engines. This lap is obtained by length- 



238 POWER PLANT TESTING 

ening or shortening the rods M, M by means of the adjusting 
nuts. 

Now place the exhaust valves e, e, by lengthening or short- 
ening the rods N, N by means of the adjusting nuts in a position 
so that the working edges will just open the exhaust ports, 
or, in other words, place the lines g and h nearly in line with 
each other. Some engineers prefer a slight amount of lap, 
others prefer a slight opening of the exhaust ports when the 
valves are in this position; under these conditions the lines 
g and h cannot be in line, but will stand apart, as indicated 
in the illustration; the distance between these lines will, of 
course, be equal to the desired amount of opening; for small 
engines it is about fg inch, and for larger engines may be 
increased to ^ inch, but in any case the amount of this 
opening should be less than the lap of the steam valves, other- 
wise there will be danger of steam blowing through. 

The paper between the wrist plate and the washer on the 
supporting pin should now be taken out, so that the wrist 
plate connected to the valves can be swung on its pin. 

The next step will be to pay some attention to the rocker 
arm. Set this arm in a vertical position by means of a plumb- 
line, and connect the eccentric rod to it ; then turn the eccentric 
around on the shaft, and see that the extreme points of travel 
are at equal distances from the plumb-line. To secure this 
a little adjustment in the stub end of the eccentric rod may 
be necessary. Now connect the hook rod I to its pin on the 
wrist plate, and again turn the eccentric around on the shaft, 
and thus determine the extreme points of travel of the wrist 
plate. If all parts have been correctly adjusted, the line d 
will coincide with the lines f, f at the extreme points of travel; 
if this is not the case, the hook rod will have to be adjusted 
at its stub end so as to obtain the desired equalized motion 
of the wrist plate. 

The next step will be to set the valves correctly with the 
position of the crank; to do so the lengths of the rods M, M, N, 
and N must not be changed, but the following mode of pro- 
cedure should be followed : Place the crank on one of its dead- 
centers, and turn the eccentric loosely on the shaft in the 
direction in which the engine is to run, until the steam valve 
nearest to the piston shows an opening or lead of ^ to £ inch, 



STEAM ENGINE TESTING 239 

according to size of engine, the smaller lead, of course, being 
adopted for small engines. After the proper lead has been 
given to this valve, secure the eccentric, and turn the shaft 
with eccentric in the same direction in which the engine is 
to run until the crank is on the opposite dead-center, and 
notice if the opening or lead at this end of the cylinder is 
the same as on the other steam valve; if not, shorten or 
lengthen slightly, as may appear necessary, the connection 
between wrist plate and eccentric; of course much adjust- 
ment in the length of these connections is not admissible with- 
eout rsetting the valves with reference to the wrist plate. 

The only thing which now remains to be done is to adjust 
the cam rods G, G. To do so, secure the governor balls in 
their highest position, and disconnect the hook rod from wrist 
pin; lengthen or shorten the cam rods G, G, so as to bring 
the detachment apparatus into action, swing the wrist plate 
back and forward and make such adjustment in the rods G, G, 
as to permit the steam valves to be released when the steam 
port has been opened about J inch. This adjustment is for 
the purpose of keeping the engine under the control of the 
governor, in case, for some reason or another, the load on 
the engine is suddenly thrown off. After this adjustment the 
governor balls should be placed in their lowest position, in 
which the releasing gear should not detach the steam valves, 
but allow the steam to follow nearly full stroke. Sometimes 
the releasing gear is constructed in such a manner as to close 
the steam valves automatically, in case the belt leading to 
the governor should be broken, or the load on the engine 
suddenly thrown off. In cases of this kind the governor balls 
need not be placed in their highest position, but should be 
placed in their lowest position, and the wrist plate moved to 
either end of its extreme travel; the steam port opposite this 
end of travel of wrist plate will then-be wide open; now adjust 
the corresponding cam rod so that the releasing gear is nearly 
on the point of releasing the valve; then move the wrist plate 
to other end of its extreme travel, and adjust the other 
cam rod in the same manner. To prove the correctness of 
the cut-off adjustment, raise the governor balls to about a 
position where they would be when at work, or to a medium 
height, and block them there ; then, with the connection made 



240 POWER PLANT TESTING 

between the eccentric and the wrist plate, turn the engine 
shaft slowly in the direction in which it is to run, and when 
the valve is released measure upon the slide the distance 
through which the cross-head has moved from its extreme 
position. Continue to turn the shaft in the same direction, 
and when the other valve is released, measure the distance 
through which the cross-head has moved from its extreme 
position, and if the cut-off is equalized, these two distances 
will be equal to each other. If they are not, adjust the length 
of the cam rods until the points of cut-off are at equal dis- 
tances from the beginning of the stroke. Replace the back 
bonnets and see that all connections have been properly made, 
which will complete the setting of the valves. Wherever 
convenient, it is desirable that an indicator be applied to the 
engine when at work, and the setting of the valves tested. 
If necessary, they should be readjusted for the best possible 
condition for economical work. 

Clearance Determination of an Engine. This test is made 
usually to determine the clearance volume of a steam or a gas 
engine. It is sometimes important to know the clearance 
volume of an engine, as it materially affects the expansion 
curve of the engine. If it is too large it causes an excessive 
loss in the engine. The clearance volume is also necessary if 
a theoretical expansion curve is to be constructed. 

The engine is first set on dead-center with the piston at the 
head end of the cylinder. This is done by the " method of 
trammels " (see footnote, page 231). Then the steam chest 
cover and valve are to be removed and a rubber gasket under 
a block of wood is placed over both steam-port openings in 
the valve seat and bolted on. Usually candle wicking must 
be packed around the piston to stop excessive leakage. For 
this purpose the cylinder head must be removed and again 
replaced. 

Two vessels filled with clean water should be provided and 
weighed. The clearance space is to be filled from one vessel, 
the time required being taken. As soon as the space is filled 
the first vessel is removed and the space is kept filled with 
water from the other vessel for five minutes. The vessels are 
then again weighed and the water used from each of them deter- 
mined. The average rate of leakage while filling the space is 



STEAM ENGINE TESTING 241 

usually assumed to be one-half the rate of leakage when full of 
water as during the leakage test. 

If w x = weight in pounds to fill the clearance space, / minutes = 
the time required to fill the clearance space, and w 2 = the weight 
of water in pounds necessary to keep it full for one minute ; 
then the leakage during filling is 

w' = —Xt, 

2 

and the clearance = (wi—w f ) in pounds of water, which can be 
readily reduced to cubic inches. 

The clearance for the crank end is found in the same general 
way as that for the head end. 

Most engines have small holes at the top of the cylinder 
at each end (for double-acting engines) which lead into the 
clearance space. Holes which are covered by the piston on 
the dead-center would obviously be of no value. All water 
must of course be drained from each end before filling. Remov- 
ing the cylinder head for packing the piston is the best method 
for observing with certainty that there is no water in the head 
end. The drip pipes in the cylinder can usually be relied on 
to remove water from the crank end. Determinations should 
be repeated several times, and the average value is to be used in 
calculations. 



RULES FOR CONDUCTING STEAM ENGINE TESTS 

An elaborate report has been published by the American 
Society of Mechanical Engineers entitled " Rules for. Conducting 
Steam Engine Tests." 1 In this report the rules regulating 
standard commercial tests of engine plants, including auxiliary 
machinery, are given in great detail. Every engineer should 
have available a copy of these rules. It is impracticable to 
print in this book the complete report, but space will be taken 
to give the most important parts. 

1 This report is issued in a pamphlet of 78 pages and can be obtained 
at at small cost from the Secretary of the American Society of Mechanical 
Engineers, Engineering Society's Building, New York city. It is 
printed complete in the Transactions of the Society, Vol. 24, pages 713- 
846. 



242 POWER PLANT TESTING 

One of the most important subjects discussed is in regard 
to the definition of the " Heat consumption " of an engine 
plant. This is to be determined by measuring the quantity of 
steam consumed by the plant, calculating the total heat of the 
entire quantity and crediting this total with that portion of 
the heat rejected by the plant which is utilized and returned 
to the boiler. " Engine plant " as used in this report should 
include the entire equipment of the steam plant producing 
power ; that is, the main cylinder or cylinders, the steam jackets 
and reheaters, the air, circulating and boiler-feed pumps if 
steam driven, and any other machinery driven by steam required 
for the operation of the engine. That the engine plant should 
be charged with the steam used by all the auxiliary machinery 
in determining the plant economy is necessary because the steam 
consumption of the engine is finally benefited, or at least it 
should be, by the heat they return to the system. It is, of 
course, now the general practice in commercially operated 
plants to pass the exhaust steam from auxiliaries operated 
non-condensing, through a feed-water heater, thus carrying 
back to the boiler a great deal of the heat. 

When a plant is operating non-condensing, discharging the 
steam into the atmosphere, or with a jet condenser, the steam 
consumption of the engine cannot be determined by weighing 
or measuring the steam used as can be done when a surface 
condenser is used. The method followed in this case is to 
determine the steam used by the weight of water supplied 
to the boiler, assuming, of course, that all the steam from the 
boiler or boilers used goes to the engine tested. It can usually 
be arranged for a test of one of the engines in a large plant 
that one or more boilers can be segregated or cut off in the piping 
connections so that these boilers alone supply the engine. 
When, however, this method is to be used it is necessary to 
determine by a separate test the leakage of the boiler and of 
the piping from the boiler to the throttle valve of the engine. 
This leakage, of course, is the amount of feed-water pumped 
into the boiler to keep the level in the water gage constant 
without taking away any more steam than is lost in this way. 
When determining this leakage, the pressure in the boiler 
must be maintained the same as that at which steam is to be 
supplied to the engine for its test. The feed-water pumped 



STEAM ENGINE TESTING 243 

into the boiler supplying the engine less the boiler and pipe 
leakage will be the net amount of steam used by the engine. 

Surface condensers are usually perferred for accurate engine 
tests because the steam used by the engine can be determined 
directly by weighing or measuring the condensed steam. A 
surface condenser is essentially a vessel of considerable size 
in which there are a great many brass tubes. It is usually 
designed so that exhaust steam passes on its way through the 
condenser into contact with the outside surface of these tubes 
while cold water for condensing the steam circulates inside the 
tubes. Steam condensed in this way accumulates in the bottom 
of the condenser and is removed by an air pump used for pro- 
ducing a vacuum, or by gravity if the pressure in the condenser 
is atmospheric, as it will be if the engine is operating " non- 
condensing," that is, without a vacuum. It is very essential, 
however, that surface condensers be tested for leakage, preferably 
before and after every important test is made ; and the leakage 
should be determined with the same vacuum in the condenser 
as there is when it is used in the engine test. Probably 
the best method to determine the amount of condenser leakage 
is to pass cooling water through the tubes at the normal rate 
of flow, maintaining at the same time with the air pump the 
required vacuum. Then the amount of water removed by the 
air pump is the leakage of circulating water through the tubes 
into the steam space. Under normal operating conditions 
there would be no leakage of steam into the circulating water, 
because the water will be at higher pressure than the steam. 

If only a test is to be made to determine whether or not 
there is any leakage in the condenser, the test most generally 
applied is to close all connections to the condenser and observe 
whether a vacuum once established can be maintained a reason- 
ably long time. A more rapid test, applicable, however, only 
where salt water is used for cooling, is to test the condensed 
steam several times during a test by adding a little silver nitrate 
to a small amount of the condensed steam. If there is no 
appreciable precipitate x it may be assumed that the condenser 
does not leak. 

Some of the important considerations to be observed in an 

1 The white precipitate formed with the salt in sea water is of course 
silver chloride, thus, AgN0 3 + NaCl = AgCl + NaN0 3 . 



244 POWER PLANT TESTING 

accurate engine test will now be given as stated in the rules 
adopted by the American Society of Mechanical Engineers. 

General Conditions of Plant. Examine the engine and the 
entire system of piping concerned in the test; note its general 
condition and any points of design, construction, or operation 
which bear on the objects in view. Make a special examination 
of the valves and pistons for leakage by applying the working 
pressures with the engine at rest, and observe the quantity of 
steam, if any, blowing through per hour. 

Dimensions, etc. Measure the dimensions of the cylinders 
of the engine when it is hot. If they are much worn, the 
average diameter should be determined. Measure also the 
clearance, which should be done, if possible, by filling the spaces 
with water previously measured, the piston being placed at 
the end of the stroke (see page 240). If the clearance cannot 
be measured directly, it can be determined approximately from 
the working drawings of the cylinder. 

Calibration of Instruments. All instruments and apparatus 
should be calibrated and their reliability and accuracy verified 
by comparison with recognized standards. 

Leakages of Steam, Water, etc. In all tests except those 
of a complete plant made under conditions as they exist, the 
boiler and its connections, both steam and feed, as also the steam 
piping leading to the engine and its connections, should, so far 
as possible, be made tight. All connections should, so far as 
possible, be visible and be blanked off, and where this cannot 
be done, satisfactory assurance should be obtained that there 
is no leakage either in or out. 

Duration of Tests. The duration of a test should depend 
largely upon its character and the objects in view. The standard 
heat test of an engine, and, likewise, a test for the simple deter- 
mination of the feed-water consumption, should be continued 
for at least five hours, unless the class of service precludes a 
continuous run of so long duration. It is desirable to con- 
tinue the test, the number of hours stated to obtain a number 
of consecutive hourly records as a guide in analyzing, the reliabil- 
ity of the whole. 

The commercial test of a complete plant, embracing boilers 
as well as engine, should continue at least one full day of twenty- 
four hours, whether the engine is in motion during the entire 



STEAM ENGINE TESTING 245 

time or not. A continuous coal test of a boiler and engine should 
be of at least ten hours' duration, or the nearest multiple of 
the interval between times of cleaning fires. 

Starting and Stopping a Test. (a). Standard Heat Test and 
Feed-water Test of Engine. The engine having been brought 
to the normal condition of running, and operated a sufficient 
length of time to be thoroughly heated in all its parts, and the 
measuring apparatus having been adjusted and set to work, 
the height of water in the gage glasses of the boilers is observed, 
the depth of water in the reservoir from which the feed water 
is supplied is noted, the exact time of day is observed, and the 
test held to commence. Thereafter the measurements deter- 
mined upon for the test are begun and carried forward Until 
its close. If practicable, the test may be commenced at some 
even hour or minute, but it is of first importance to begin at 
such time as reliable observations of the water heights are 
obtained, whatever the exact time happens to be when these 
are satisfactorily determined. When the time for the close 
of the test arrives, the water should, if possible, be brought 
to the same height in the glasses and to the same depth in the 
feed-water reservoir as at the beginning, delaying the conclusion 
of the test, if necessary, to bring about this similarity of condi- 
tions. If differences occur, the proper corrections must be made. 

(b). Complete Engine and Boiler Tests. For a continuous 
running test of combined engine or engines, boiler or boilers, 
the same directions apply for beginning and ending the feed- 
water measurements as those just referred to. The time of 
beginning and ending such a test should be the regular time of 
cleaning the fires, and the exact time of beginning and ending 
should be the time when the fires are fully cleaned, just prepar- 
atory to putting on fresh coal. 

For a commercial test of combined engine and boiler, whether 
the engine runs continuously for the full twenty-four hours of 
the day, or only a portion of the day, the fires in the boilers 
being banked during the time when the engine is not in motion, 
the beginning and ending of the test should occur at the regular 
time of cleaning the fires, the method followed being that given 
above. In cases where the engine is not in continuous motion, 
as, for example, in textile mills, where the working time is ten 
or eleven hours out of twenty-four, and the fires are cleaned 



246 POWER PLANT TESTING 

and banked at the close of the day's work, the best time for 
starting and stopping a test is the time just before banking, 
when the fires are well burned down and the thickness and 
condition can be most satisfactorily judged. 

Measurements of Heat Units Consumed by the Engine. 
The measurements of the heat consumption require the measure- 
ment of each supply of feed-water to the boiler — that is the 
water supplied by the main feed pump, that supplied by auxil- 
iary pumps, such as jacket water, water from separators, drips, 
etc., and the water supplied by gravity and other means; also 
the determination of the temperature of the water supplied from 
each source, together with the pressure and quality of the 
steam. The temperatures at the various points should be those 
applying to the working conditions. 

The heat to be determined is that used by the entire engine 
equipment, embracing the main cylinders and all auxiliary 
cylinders and mechanism concerned in the operation- of the 
engine, including the air pump, circulating pump, feed pumps, 
also the jacket and reheater, when these are used. 

The steam pressure and the quality of the steam are to 
be taken at some point conveniently near the throttle valve. 
The quantity of the steam used by the calorimeter must be 
determined and properly allowed for. 

Measurement of Feed-water or Steam Consumption of 
Engine, etc. The method of determining the steam consump- 
tion applicable to all plants is to measure all the feed-water 
supplied to the boilers, and deduct therefrom the water dis- 
charged by separators and drips, as also the water and steam 
which escapes on account of leakage of the boiler and its pipe 
connections and leakage of the steam main and branches con- 
necting the boiler and the engine. In plants where the engine 
exhausts into a surface condenser the steam consumption can 
be measured by determining the quantity of water discharged 
by the air pump, corrected for any leakage of the condenser, 
and adding thereto the steam used by jackets, reheaters, and 
auxiliaries as determined independently. 

The corrections or deductions to be made for leakage above 
referred to should be applied only to the standard heat-unit 
test and tests for determining simply the steam or feed-water 
consumption, and not to coal tests of combined engine and 



STEAM ENGINE TESTING 247 

boiler equipment. In the latter, no correction should be made 
except for leakage of valves connecting to other engines and 
boilers, or for steam used for purposes other than the operation 
of the plant under test. Losses of heat due to imperfections 
of the plant should be charged to the plant, and only such 
losses as are concerned in the working of the engine alone should 
be charged to the engine. 

Measurement of Steam Used by Auxiliaries. It is highly 
desirable that the quantity of steam used by the auxiliaries, 
and in many cases that used by each auxiliary, should be deter- 
mined exactly, so that the net consumption of the main engine 
cylinders may be ascertained and a complete analysis made of 
the entire work of the engine plant. 

Indicated Horse Power. The indicated horse power should 
be determined from the average mean effective pressure of 
diagrams taken at intervals of twenty minutes, and at more 
frequent intervals if the nature of the test makes it necessary, 
for each end of the cylinder. With variable loads, such as 
those of engines driving generators for electric railroad work, 
and of rolling-mill engines, the diagrams cannot be taken 
too often. 

The most satisfactory driving rig for indicating seems 
to be some form of well-made pantagraph, with driving cord 
of fine annealed wire leading to the indicator. The reducing 
motion, whatever it may be, and the connections to the indicator, 
should be so perfect as to produce diagrams of equal lengths, 
when the same indicator is attached to either end of the cylinder, 
and produce a proportionate reduction of the motion of the 
piston at every point of the stroke, as proved by test. 

The use of the three-way cock and the single indicator con- 
nected to the two ends of the cylinder is not advised, except 
in cases where it is impracticable to use an indicator close to 
each end. If a three-way cock is used, the error produced by the 
increased clearance should be determined and allowed for. 

Testing Indicator Springs. To make a perfectly satis- 
factory comparison of indicator springs with standards, the 
calibrations should be made, if practicable, under the same 
conditions as those pertaining to their ordinary use. 

Brake Horse Power. This term applies to the power deliv- 
ered from the fly-wheel shaft of the engine. It is the power 



248 POWER PLANT TESTING , 

absorbed by a friction brake applied to the rim of the wheel, 
or to the shaft. A form of brake is preferred that is self adjust- 
ing to a certain extent, so that it will, of itself, tend to main- 
tain a constant resistance at the rim of the wheel. One of the 
simplest brakes for comparatively small engines, which may be 
made to embody this principle, consists of a cotton or hemp 
rope, or a number of ropes, encircling the wheel arranged with 
weighing scales or other means of showing the strain. An 
ordinary band brake may also be constructed so as to embody 
the principle. The wheel should be provided with interior 
flanges for holding water used for keeping the rim cool. 

Quality of Steam. When saturated steam is used, its qual- 
ity should be obtained by the use of a good throttling calo- 
rimeter attached to the main steam pipe near the throttle 
valve. When the steam is superheated, the amount of 
superheating should be found by the use of a thermometer 
placed in a thermometer-well filled with mercury, inserted 
in the pipe. The sampling pipe for the calorimeter should, 
if possible, be attached to a section of the main pipe having 
a vertical direction, with the steam preferably passing upward, and 
the sampling nozzle should be made of a half -inch pipe, having 
at least twenty one-eighth inch holes in its perforated surface. 

Speed. There are several reliable methods of ascertaining 
the speed, or the number of revolutions of the engine crank- 
shaft per minute. The most reliable method, and the one 
recommended, is the use of a continuous recording engine 
register or counter, taking the total reading each time that the 
general test data are recorded, and computing the revolutions per 
minute corresponding to the difference in the readings of the instru- 
ment. When the speed is above 250 revolutions per minute, 
it is almost impossible to make a satisfactory counting of the 
revolutions without the use of some form of mechanical counter. 

Recording the Data. Take note of every event connected 
with the progress of the trial, whether it seems at the time to 
be important or unimportant. Record the time of every event, 
and the time of taking every weight, and every observation. 
Observe the pressures, temperatures, water heights, speeds, 
etc., every twenty or thirty minutes when the conditions are 
practically uniform, and at much more frequent intervals 
if the conditions vary. 



STEAM ENGINE TESTING 249 

Uniformity of Conditions. In a test having for its object 
the determination of the maximum economy obtainable from 
an engine, or where it is desired to ascertain with special accuracy 
the effect of predetermined conditions of operations, it is impor- 
tant that all the conditions under which -the engine is operated 
should be maintained uniformly constant. 

Analysis of Indicator Diagrams, (a) Steam Accounted for 
by the Indicator. The simplest method of computing the 
steam accounted for by the indicator is the use of the formula 

■.M~^[(C+E)XW C -(H+B)XW*], . . (65) 

which gives the weight in pounds per indicated horse power 
per hour. In this formula the symbol M.E.P. refers to the mean 
effective pressure. In multiple-expansion engines this is the 
" combined " mean effective pressure referred to the cylinder in 
question. C is the proportion of the stroke completed at a 
point on the expansion line of the diagram near the actual 
cut-off or release, the symbol H'to the proportion of compres- 
sion, and the symbol E to the proportion of clearance; all 
of which are determined from the indicator diagram. The 
symbol W c refers to the weight of one cubic foot of steam at the 
cut-off or release pressure; and W /( to the weight of one cubic 
foot of steam at the compression pressure, these weights being 
taken from steam tables. 

The points at cut-cff and release on the expansion line and 
the point at the beginning of compression are located as shown 
on the sample diagram, Fig. 187. On the expansion and com- 
pression lines they are the points which mark the complete 
closure of the valve. The point at cut-cff lies where the curve 
of expansion begins after the rounding of the diagram due to 
throttling or " wire-drawing " which occurs when the valve 
is closing. This point of cut-off may be located on the diagram 
by finding the point where the curve is tangent to a hyperbolic 
curve. 

Should the point selected in the compression curve be at 
the same height as the point in the expansion curve, then 
W c =W/ t , and the formula becomes 

^|x(C-H) X W c) .... (66) 



250 POWER PLANT TESTING 

in which (C — H) represents the distance between the two points 
divided by the length of the diagram. 

When the load and all other conditions are substantially 
uniform, it is unnecessary to work up the steam accounted for 
by the indicator from all the diagrams taken. Five or more 
sample diagrams may be selected and the computations based 
on the samples instead of on the whole. 

(b) Sample Indicator Diagrams. In order that the report 
of a test may afford complete information regarding the con- 
ditions of the test, sample indicator diagrams should be selected 
from those taken and copies appended to the tables of results. 
In cases where the engine is of the multiple-expansion type 




Atmospheric Line 
Fig. 187. — Typical Indicator Diagram. 

these sample diagrams may also be arranged in the form of 
" combined " diagrams. 

(c) The Point of Cut-off. The term "cut-off" as applied to 
steam engines, although somewhat indefinite, is usually con- 
sidered to be at an earlier point in the stroke than the beginning 
of the real expansion line. That the cut-off point may be defined 
in exact terms for commercial purposes, as used in steam- 
engine specifications and contracts, the Committee recommends 
that, unless otherwise specified, the commercial cut-off, which 
seems to be an appropriate expression for this term, be ascer- 
tained as follows: Through a point showing the maximum 
pressure during admission, draw a line parallel to the atmos- 
pheric line. Through the point on the expansion line near the 
actual cut-off, draw a hyperbolic curve. The point where these 
two lines intersect is to be considered the point at the com- 
mercial cut-off. The percentage is then found by dividing the 



STEAM ENGINE TESTING 



251 



length of the diagram measured to this point, by the total 
length of the diagram, and multiplying the result by ioo. 

The principle involved in finding the commercial cut-off 
is shown in Figs. 188 and 189. The first represents a diagram 




G f 

Fig. 188. — Indicator Diagram from a Slow-speed Corliss Engine. 



from a slow-speed Corliss engine and the second a diagram 
from a single -valve high-speed engine. In the latter case, 
owing to the inertia or " fling " of the indicator pencil, the steam 
line is irregular and the maximum pressure is found by taking 
the mean of the vibrations at the highest part of the curve. 




Fig. 



H G F 

— Indicator Diagram from a High-speed Single-valve Engine. 



The commercial cut-off, as thus determined, is situated at 
an earlier point of the stroke than the actual cut-off referred to 
in computing the " steam accounted for " by the indicator 
on page 249. 



252 POWER PLANT TESTING 

(d) Ratio of Expansion. The commercial ratio of expansion 
for a simple engine is determined by dividing the volume cor- 
responding to the piston displacement, including clearance, 
by the volume of the steam at the commercial cut-off, including 
clearance. 

In the multiple expansion engine it is determined by divid- 
ing the net volume of the steam indicated by the low pressure 
diagram at the end of the expansion line, assumed to be con- 
tinued to the end of the stroke by the net volume of the steam 
at the maximum pressure during admission to the high pressure 
cylinder. 

The ideal ratio of expansion is the quotient obtained by 
dividing the volume of the piston displacement by the volume 
of the steam at the cut-off (the latter being referred to the 
throttle-valve pressure) less the volume equivalent to that 
retained at compression. In a multiple expansion engine the 
volumes to be used are those pertaining to the low pressure 
cylinder and the high pressure cylinder, respectively. 

(e) Diagram Factor. The diagram factor is the proportion 
borne by the actual mean effective pressure measured from the 
indicator diagram to that of a diagram in which the various 
operations of admission, expansion, release and compression 
are carried on under assumed conditions. The factor rec- 
ommended refers to an ideal diagram which represents the 
maximum power obtainable from the steam accounted for by 
the indicator diagrams at the point of cut-off, assuming first 
that the engine has no clearance; second, that there are no 
losses through wire-drawing the steam either during admission 
or release ; third, that the expansion line is a hyperbolic curve ; 
and fourth, that the initial pressure is that of the boiler and the 
back pressure that of the atmosphere for a non-condensing 
engine, and of the condenser for a condensing engine. 

In cases where there is a considerable loss of pressure between 
the boiler and the engine, as where steam is transmitted from a 
central plant to a number of consumers, the pressure of the 
steam in the supply main shpuld be used in place of the boiler 
pressure in constructing the diagrams. 

Standards of Economy and Efficiency. The hourly con- 
sumption of heat, determined by employing the actual temper- 
ature of the feed-water to the boiler, as pointed out in the 



STEAM ENGINE TESTING 253 

section entitled " Measurement of Heat Units Consumed by 
the Engine " on page 246, divided by the indicated and brake 
horse power, that is, the number of heat units consumed per 
indicated and per brake horse power per hour, are the standards 
of engine efficiency recommended by the Committee. The con- 
sumption per hour is chosen rather than the consumption per 
minute so as to conform with the designation of time applied to 
the more familiar units of coal and water measurement which 
have heretofore been used. The British standard where the tem- 
perature of the feed-water is taken as that corresponding to the 
temperature of the back-pressure steam, allowance being made 
for any drips from jackets or reheaters, is also included in the 
tables. 

It is useful in this connection to express the efficiency in 
its more scientific form, or what is called the " thermal efficiency 
ratio." The thermal efficiency ratio is the proportion which 
the heat equivalent of the power developed bears to the total 
amount of heat actually consumed, as determined by test. 
The heat converted into work represented by one horse power 
is 1, 980,0 co foot-pounds per hour, and this divided by 778 
equals 2545 B.T.U. Consequently, the thermal efficiency ratio 
is expressed by the fraction 

2 545 



B.T.U. per I.H.P. per hour' 

Heat Analysis. For certain scientific investigations it is 
useful to make a heat analysis of the indicator diagram, to 
show the interchange of heat from steam to cylinder walls, etc., 
which is going on within the cylinder. This is unnecessary for 
commercial tests. 

Entropy-temperature Diagram. The study of the heat 
analysis is facilitated by the use of the entropy-temperature 
diagram in which areas represent quantities of heat, the co-ordi- 
nates being the entropy and absolute temperature. 

Ratio of Economy of an Engine to that of an Ideal Engine. 
The ideal engine recommended for obtaining this ratio is that 
which was adopted by the Committee appointed by the Civil 
Engineers of London, to consider and report a standard thermal 
efficiency for steam engines. This engine is one which follows 
the Rankine cycle where steam at a constant pressure is admitted 



254 POWER PLANT TESTING 

into a cylinder having no clearance, and after the point of cut- 
off is expanded adiabatically to the back-pressure. In obtain- 
ing the economy of this engine the feed-water is assumed to be 
returned to the boiler at the exhaust temperature (page 261). 
returned to the boiler at the exhaust temperature. 

The ratio of the economy of an engine to that of the ideal 
engine is obtained by dividing the heat consumption per indi- 
cated horse power per minute for the ideal engine by that of 
the actual engine. 

Miscellaneous. In the case of the tests of combined engines 
and boiler plants, where the full data of the boiler performance 
are to be determined, reference should be made to the directions 
given by the Boiler Test Committee of the Society, Code 1899. 
(See pages 203-228.) 

In testing steam pumping engines and locomotives in accord- 
ance with the standard methods of conducting such tests, recom- 
mended by the Committees of the Society, reference should be 
made to the reports of those Committees in the Transactions 
American Society of Mechanical Engineers, vol. 12, page 530, 
and in vol. 14, page 131 2. 

Report of Tests. The data and results of the test should 
be reported in the manner and in the order outlined in one of 
of the following tables, the first of which gives, it is hoped, a 
complete summary of all the data and results as applied not 
only to the standard heat -unit test, but also to tests of a com- 
bined engine and boiler for determining all questions of per- 
formance, whatever the class of service. 

It is recommended that any report of a test be supplemented 
by a chart in which the data of the tests are graphically pre- 
sented. (As example of such a chart as applied to a boiler test 
see page 202.) 

DATA AND RESULTS OF STANDARD HEAT TEST OF STEAM 
ENGINE 

Arranged according to the Short Form Advised by the Engine Test 
Committee of the American Society of Mechanical Engineers. Code of 
1902. 
1. Made by on Engine located at 



Test made to determine. 
Date of Trial 



STEAM ENGINE TESTING 255 

3 . Type and class of engine ; also of condenser 

4. Dimensions of main engine: 

(a) Diameter of cylinder, inches 

(b) Stroke of piston, feet 

(c) Diameter of piston rod, inches 

(d) Average clearance, per cent 

(e) Horse power constant for one pound mean effective pressure 
and one revolution per minute 

5. Dimensions and type of auxilaries 



TOTAL QUANTITIES, TIME, ETC. 

6. Duration of test, hours 

7. Total water fed to boilers from main source of supply, lbs. . . . 

8. Total water fed from auxiliary supplies: 

(a) " . . . 

(b) " ... 

(c) " . . . 

9. Total water fed to boilers from all sources " 

0. Moisture in steam or superheating near throttle. ... % or deg. 

1. Factor of correction for quality of steam 

2. Total dry steam consumed for all purposes lbs. . . . 



HOURLY QUANTITIES 

13. Water fed from main source of supply per hour, lbs 

14. Water fed from auxiliary supplies: " " " 

(a) " 

(b) " 

(c) " 

15. Total water fed to boilers per hour " 

16. Total dry steam consumed per hour " 

17. Loss of steam and water per hour due to drips from main steam 

pipes and to leakage of plant lbs 

18. Net dry steam consumed per hour by engine and auxiliaries, lbs 



PRESSURES AND TEMPERATURES (CORRECTED) 

19. Pressure in steam pipes near throttle by gage lbs. per sq. in 

20. Barometric pressure of atmosphere in inches of mercury, ins 

21. Pressure in receivers by gage lbs. per sq. in 

22. Vacuum in condenser in inches of mercury ins 

23. Pressure in jackets and reheaters by gage lbs. per sq. in 

24. Temperature of main supply of feed- water deg. F 

25. Temperature of auxiliary supplies of feed-water: 

(a) " 

(b) " 

(c) " 

26. Ideal feed- water temperature corresponding to the pressure of steam 

in the exhaust pipe, allowance being made for the heat derived 
from the jacket or reheater drips deg. F 



256 



POWER PLANT TESTING 



DATA RELATING TO HEAT MEASUREMENTS 

Heat units per pound of feed-water, main supply B.T.U. . . 

Heat units per pound of feed- water, auxiliary supplies: 

(a) 

(b) 



(c) 



43- 



45- 



Heat units consumed per hour, main supply 

Heat units consumed per hour, auxiliary supplies : 

(a) 

(b) 

(c) .... 

Total heat units consumed per hour for all purposes 

Loss of heat per hour due to leakage of plant, drips, etc. 
Net heat units consumed per hour: 

(a) By engine alone 

(b) By auxiliaries 

Heat units consumed per hour by engine alone, reckoned from 

temperature given in item 26 B.T.U 

INDICATOR DIAGRAMS 

Commercial cut-off in per cent of stroke 

Initial pressure lbs. per sq. in. above atmosphere 

Back pressure at mid stroke above or below atmosphere, in pounds 

per square inch 

Mean effective pressure in pounds per square inch 

Equivalent M.E.P. in pounds per square inch: 

(a) Referred to first cylinder 

(b) Referred to second cylinder 

(c) Referred to third cylinder 

Pressures above zero in pounds per square inch : 

(a) Near cut-off 

(b) Near release 

(c) Near beginning of compression 

Percentage of stroke at points where pressures are measured: 

(a) Near cut-off 

(b) Near release 

(c) Near beginning of compression r 

Steam accounted for by indicator in pounds per I.H.P. per hour: 

(a) Near cut-off 

(b) Near release 

Ratio of expansion (page 252): 

(a) Commercial 

(b) Ideal 

SPEED 

Revolutions per minute 

POWER 
Indicated horse power developed by main engine cylinders : 

First cylinder • 

Second cylinder 

Third cylinder 

Total 

Brake horse power developed by engine 



STEAM ENGINE TESTING 257 

STANDARD EFFICIENCY AND OTHER RESULTS 

46 Heat units consumed by engine and auxiliaries per hour: 

(a) Per indicated horse power, B.T.U 

(b) Per brake horse power, B.T.U 

47. Equivalent standard coal in pounds per hour: 

(a) Per indicated horse power, pounds 

(b) Per brake horse power, pounds 

48. Heat units consumed by main engine per hour corresponding to ideal 

maximum temperature of feed water given in item 26: 

(a) Per indicated horse power, B.T.U 

(b) Per brake horse power, B.T.U 

49. Dry steam consumed per indicated horse power per hour: 

(a) Main cylinders, including jackets, pounds 

(b) Auxiliary cylinders, pounds 

(c) Engine and auxiliaries, pounds 

50. Dry steam consumed per brake horse power per hour: 

(a) Main cylinders, including jackets, pounds 

(b) Auxiliary cylinders, pounds 

(c) Engines and auxiliaries, pounds 

51. Percentage of steam used by main engine cylinders accounted for by 

indicator diagrams, near cut-off of high pressure cylinder, %. 

ADDITIONAL DATA 

Add any additional data bearing on the particular objects of the test 
or relating to the special class of service for which the engine is used. Also 
give copies of indicator diagrams nearest the mean, and the corresponding 
scales. 



Heat Balance. The importance of checking tests of engines 
cannot be too strongly stated. An important aid for deter- 
mining the correctness of such tests is obtained by calculating 
a heat balance, which is making a balance sheet showing the 
heat received and rejected by the engine. Only such tests 
should be considered satisfactory which show a reasonable 
agreement in the heat balance. In ordinary commercial test- 
ing by experienced engineers a heat balance is not often calcu- 
lated, but for accurate laboratory work it should always be 
made out. It shows at a glance how much heat energy is 
received by the engine and what disposition is made of it. 

In a heat balance the heat supplied to the engine will be 
accounted for in the following items: (1) Heat equivalent 
of useful work as calculated from brake horse power. (2) Heat 
equivalent of engine friction. (3) Heat discharged in the con- 
densed steam (into hot well). (4) Heat absorbed by cooling 
water. (5) Heat radiated and other losses (by difference). 



258 POWER PLANT TESTING 

Heat supplied to the engine per minute Q =pounds of steam 
supplied to engine per minute times the total heat in a pound 
of steam (q x +xi ri), for wet steam and Hi +c p (t' — ti) for super- 
heated steam. The terms q 1; x 1} r 1} Hi and ti represent as in 
other equations in this book respectively the heat of the liquid, 
the quality, the heat of vaporization, the total heat, and the 
temperature, all corresponding to the pressure of the steam 
supplied. The other term t' is the temperature of the super- 
heated steam as observed by a thermometer in the steam pipe. 

Heat equivalent of the useful work done (Q M ) per minute is 
the product of the brake horse power (B.H.P.) and the constant 
33, ceo divided by the mechanical equivalent of a B.T.U. ; that is, 

B.H.P X33.000 

778 

Similarly, the heat equivalent of the engine friction (Q/) per 
minute is expressed by 

F.H.PX33.000 

778 

where F.H.P. is the friction horse power or the difference between 
the indicated 1 and the brake horse power. 

Heat discharged in the exhaust to the hot-well may be repre- 
sented by 

Q e = pounds of steam per minute times the heat of the liquid 
at the temperature of the exhaust. Or for practical purposes 
this is the same as taking the product of the pounds of steam 
per minute and the temperature of the exhaust (condensed 
steam) in degrees Fahrenheit less 32. 

The heat absorbed in the cooling water per minute is then 

Q c =pounds of cooling water per minute times the difference 
between the heat of the liquid at the outlet and inlet. For 
the small difference in temperature occurring in the cooling 
water of engine tests we may take in place of the difference of 
the heats of the liquid the difference of the corresponding tem- 
peratures, or approximately, 

1 Often it is preferred, to express the indicated work in the heat bal- 
ance instead of the two items useful work and engine friction. Then the 

r , • -,- , , LH.P.X 3^000 

heat equivalent of the indicated work Q,= 



;STEAM ENGINE TESTING 259 

Q c = pounds cooling water per minute times the difference 
between outlet and inlet temperatures. 

Heat radiated and other Q r losses is found, by taking the 
difference between the heat supplied Q and the sum of the 
several items Q u , Qf, Q e and Q c . 

There is no "standard" method for calculating a heat 
balance. Some engineers prefer to take for the base of com- 
parison; that is, the heat supplied, the total heat of the steam 
less q 2 , the heat of the liquid in the condensed steam (at the 
temperature of the exhaust) . With this value for the heat 
supplied the item Q e drops out and the net heat supplied, 

Q M = q 1 +x 1 r 1 -q 2 = Q w +Q / + Q f +Q r . 

HEAT BALANCE 

B.T.U. B.T.U. 

per min. per min. Per cent. 

Heat supplied to the engine, Q> Heat equivalent of 

Useful work Q u 



Heat equivalent 

Engine friction Q/ 
Heat discharged 

in exhaust G>. . . . 
Heat absorbed by 

Cooling Water Q c . 
Heat Radiated and 

Other losses Or. . . 



Total, . Total, ioo 

Obviously the totals on the left- and right-hand sides of 
this balance sheet must be the same. 

Thermal Efficiency. The ratio of the heat converted into 
work to the heat supplied to the engine is called the thermal 
efficiency. The first of these quantities is calculated from the 
indicated horse power and the latter from the weight and total 
heat per pound of the steam supplied. The only uncertainty 
arises as to the proper base from which to calculate. The total 
heat of steam given in steam tables is calculated from 32 degrees 
Fahrenheit, but it is obvious if this base is adopted the engine 
may be charged with more than its share of heat. If, for 
example, the exhaust steam from the engine passes through a 
feed-water heater and that the engine returns the condensed 
steam to the boiler as feed-water at say 1 50 degrees Fahrenheit, 



260 POWER PLANT TESTING 

then there will be 1 50 — 3 2 , or 1 1 8 B . T. U . in every pound of steam 
passing continually from the engine to the boiler and from the 
boiler back to the engine without doing any work. More 
accurately, then, the thermal efficiency of an engine (E,) should 
be stated as 

E <=— n — j (09) 

V« 

where Q u and Qf as before are the heat equivalents respectively 
of the useful work and of the engine friction, while Q n should 
be defined as the net heat supplied to the engine. From this 
discussion it follows that the more efficient the feed-water heater 
is the higher the efficiency of the engine will be, and if an efficient 
heater is not used there is no reason for charging a loss to the 
engine. Obviously the limit to the amount of heat returnable 
to the boiler by means of a heater is the amount of heat in the 
exhaust steam, and this limit can be nearly approached under 
actual practical conditions. It is, therefore, very reasonable 
that the "'datum " for the calculation of the heat supplied to 
the engine should be the heat of the liquid corresponding to the 
temperature of the steam in the exhaust pipe from the engine. 
All this applies, of course, equally well to engines whether operat- 
ing condensing or non-condensing. In other words, the net 
heat supplied to the engine is the total heat of the steam enter- 
ing the engine, less the heat of the liquid at the temperature 
of the engine exhaust. 

The temperature of the exhaust must be taken by a ther- 
mometer in a suitable thermometer cup placed in the exhaust 
pipe close to the engine; and, similarly, the temperature and 
quality of the steam supplied to the engine must be determined 
by thermometers and a steam calorimeter placed close to but 
on the boiler side of the engine throttle valve. 

Engine Performance Expressed in British Thermal Units. 
A method which is rapidly gaining in favor among practical 
engineers is to express the performance of a steam engine or 
turbine by the number B.T.U., supplied, per indicated horse 
power per minute, the heat units supplied per minute being 
determined, as explained in the preceding paragraphs ; that is, the 
total heat in the steam entering at the throttle less the heat of 
the liquid at the temperature of the exhaust. (See page 287.) 



STEAM ENGINE TESTING 



261 



Engine Performance Compared with the Rankine Cycle. 

In order to know how much the efficiency of an engine can be 
improved it is most desirable to compare the actual thermal 
efficiency as defined on page 259, with the highest possible 
efficiency. For steam engines the standard cycle for comparison 
is now generally taken as the Rankine or Clausius cycle, 1 in 
which the operation of the engine is assumed to be perfect ; that 
is, without clearance in the cylinder, initial condensation, leakage 
or radiation. The indicator diagram for the Rankine cycle is 
represented by Fig. 190. The steam is assumed to be supplied 
to the engine cylinder at constant pressure until the point of 
cut-off, after which it is expanded adiabatically down to the back 
pressure at which the engine is operated on the return stroke 




Fig. 



>■ Volume 

.90. — Indicator Diagram for the Ideal Rankine or Clausius Cycle. 



when the exhaust steam is swept out of the cylinder and returned 
as feed-water to the boiler at the temperature of the exhaust. 
The same Rankine cycle represented in Fig. 190 when shown 
by a so-called entropy-temperature diagram can be made simpler 
both for analysis and calculations. This other kind of diagram, 
the details of which are somewhat more difficult to understand, 
is universally used by steam turbine engineers and has for the 
problem in hand . particular advantages. In this diagram, 
which will be now described, any surface represents accurately 



1 Years ago it was not unusual to make this comparison with the 
efficiency of the Carnot cycle as a basis. This efficiency of a heat engine, 
it will be remembered, is expressed by the ratio of T l — T 2 to 7\ where 
7\ is the absolute initial temperature and T 2 is the absolute final tem- 
perature. 



262 



POWER PLANT TESTING 







V 


,-.800 








4 


jj| 




3 600 


- 


lll« 




2 




11111 




a> 








a 








S 




^§§■§1^ 




£400 




^llllll 




2 




HHH^ 




3 

J 100 

< 


- 


III 







I) 


, , 


c 



1.0 
Entropy ( ji ) 

Fig. 191. — A Simple Entropy-tem- 
perature Diagram. 



to given scales, a quantity of heat. Absolute temperatures (T) 
are the ordinates, and entropies 1 ((f)) are the abscissas. 

Fig. 191 shows a simple heat diagram laid out with absolute 
temperature and entropy for the co-ordinates. Steam at a 

certain condition of tempera- 
ture and entropy is repre- 
sented here by the point A. 
Then if some heat is added, 
increasing both temperature 
and entropy, the final condi- 
tion is represented by the 
point B, and the area ABCD 
represents the heat added 
in passing from the condition 
at A to the condition at B. 
Such a diagram is usually 
called an entropy-temperature 
diagram, although the name 
heat diagram would probably 
be more appropriate, since 
every area represents a definite amount of heat. 

Another entropy-temperature diagram is shown in Fig. 192, 
representing by the various shaded areas the heat added to 
water at 32 degrees Fahrenheit to completely vaporize it at the 
pressure P^ The unshaded area under the irregular curve 
AB represents the heat in a pound of water at the freezing 
point (32 degrees Fahrenheit or 492 degrees in absolute tem- 
perature). The area OBCD is the heat added to the water 
to bring it to the temperature of vaporization, or in other 
words, this last area represents the heat of the liquid (q) given 
in the steam tables for the pressure P^ Further heating after 

Entropy, which Perry calls the "ghostly quantity," has no real 
physical significance, so that complete definition is not possible. If dQ is 
a small amount of heat added to a body and T is the absolute temperature 
at which the heat is added; then the change in entropy of that body is 
dQ/T, or d<f> — dQ/T. Entropy of saturated steam above the entropy of 
water at the freezing point is easily calculated. For saturated steam at 
any pressure, then <£ =xr/T + 6, where % is the quality of the steam, r is 
the heat of vaporization, T is the absolute temperature, and d is the 
entropy of the liquid (water). 

The symbols used here are those given in Peabody's Steam and Entropy 
Tables (1909). 



STEAM ENGINE TESTING 



263 



vaporization begins is at the constant temperature Ti corre- 
sponding to the pressure Pi, and is represented by an increas- 
ing area tinder line CE. When ' ' steaming ' ' is complete, the 
latent heat, or the heat of vaporization (r), is the area DCEF. 
If after all the water is vaporized more heat is added, the 
steam becomes superheated, and the additional heat required 
would be represented by an area to the right of EF. 

The use of the entropy-temperature diagram in exhibiting 
the behavior of steam during expansion will now be discussed 
and illustrated with a practical example. 




1.0 1.5 2.0 Entropy ($) 

Fig. 192. — Entropy-temperature Diagram Showing Total Heat in a 
; Pound of Dry Saturated Steam. 

Fig. 193 illustrates the heat process going on when feed-water 
is received in the boilers of a power plant at 100 degrees Fahren- 
heit, is heated and converted into steam at a temperature of 
400 degrees Fahrenheit, and then loses heat in doing work. 
When the feed-water first enters the boiler its temperature 
must be raised from ico to 400 degrees Fahrenheit, before any 
" steaming " begins. The heat added to the liquid is the area 
MNCD. This area represents the difference between the heat 
of the liquid of steam at 400 degrees Fahrenheit (q c ) and at 100 
degrees Fahrenheit (q n ) and is about 306 B.T.U. The hor- 
izontal or entropy scale shows that the difference in entropy 
between water at 100 and 400 degrees Fahrenheit, is about .436. 1 

1 As actually determined from Peabody's Steam Tables, pp. 2 and 



264 



POWER PLANT TESTING 



Every reader should understand how such a diagram is con- 
structed and especially how the curves are obtained. In this 
case the curve NC is constructed by plotting from the steam 
tables the values of the entropy of the liquid (usually marked 
with the symbol d) for a number of different temperatures 
between ioo and 400 degrees Fahrenheit. 

If now water at 4C0 degrees Fahrenheit is converted into 
steam at that temperature, the curve representing the change 
is necessarily a constant temperature line and therefore a 




Entropy {<p) 

Fig. 193. — Entropy- temperature Diagram Representing Heat Added 
Above Feed-water Temperature. 



horizontal, CE. Provided the vaporization has been complete 
the heat added in the " steaming " process is the latent heat 
or heat of vaporization of steam (r) at 400 degrees Fahrenheit, 
which is approximately 830 B.T.U. 

The change in entropy during vaporization is, then, the heat 
units added (830) divided by the absolute temperature at which 
the change occurs (400 +460 =860 degrees Fahrenheit absolute) 
or 

r 830 



T 860 



= .965. 



10, the difference in entropy is .565— .129, or .436. Practically it 
impossible to construct the scales in this small figure very accurately. 



STEAM ENGINE TESTING 265 

The total entropy of steam completely vaporized at 400 degrees 
Fahrenheit, is, therefore, the sum of the entropy of the liquid 
(water) .565 and the entropy of the steam .965, or 1.530. 1 
To represent then by CE this condition of the steam, the point 
E is plotted where entropy measured on the horizontal scale is 
1.530, as shown in the figure. 2 The area MNCEF represents then 
the total heat added to a pound of feed-water at 100 degrees 
Fahrenheit, to produce steam at 400 degrees Fahrenheit, and 
the area OBCEF represents, similarly, the total heat (H in the 
steam tables) in a pound of steam at 400 degrees Fahrenheit 
above that in water at 32 degrees Fahrenheit. 

Adiabatic Expansion and Available Energy. The practical 
example illustrated by Fig. 194 will also be used to explain 
how the entropy-temperature diagram can be used to show 
how much work can be obtained by a theoretically perfect 
engine from the adiabatic expansion of a pound of steam. When 
steam expands adiabatically — without a gain or loss of heat — 
its temperature falls. Remembering that areas in the entropy- 
temperature diagram represent quantities of heat and that in this 
expansion there is no exchange of heat, it is obvious that the 
area under a curve of adiabatic expansion must be zero; and 
this condition can be satisfied only by a vertical line which is 
a line of constant entropy. 3 For the case in Fig. 194, the expan- 
sion curve will lie, therefore, along the line EF, and if the tem- 
perature falls to 100 degrees Fahrenheit, the expansion will 
be from E to G, and during this change some of the steam has 
been condensed. If now heat is removed from this mixture 



1 Entropy, like the total heat (H) , and the heat of the liquid (q) , is 
measured. above the condition of freezing water (32 degrees Fahrenheit). 

2 The point E is shown located on another curve ST, which is deter- 
mined by plotting a series of points calculated the same as E, but for 
different pressures. If more heat had been added than was required 
for vaporization, the area DCEF would have been larger and E would 
have fallen to the right of ST, indicating by its position that the steam 
had been superheated. The curve ST is therefore a "boundary line" 
between the saturated and superheated conditions. This curve can 
also be plotted from the values obtained from a table of the entropy 
of dry saturated steam. 

3 Since in an adiabatic expansion there is n T o change of entropy, 
lines of constant entropy, in practice, are often called " adiabatics." 
It is very rare in steam turbine work that an expansion departs far 
from the adiabatic. 



266 



POWER PLANT TESTING 



of steam and water till all the steam is reduced to the liquid 
state, but without further lowering of the temperature, the 
horizontal line GN x will present the change in its condition. 
The quantity of heat rejected in this last process — technically 
known as condensing the steam — is represented by the area 
MNGF, and the heat converted into work is, therefore, the area 
NCEG; and this is called the available energy. By means of 




Entropy (</>) 
Fig. 194. — Entropy-temperature Diagram Illustrating the " Available 
Energy '•' in Steam. 

diagrams like those in the preceding figures, it will now be shown 
how the available energy of dry saturated steam for any given 



1 That the steam might be dry and saturated, the expansion would 
have had to follow the curve ET and G would have appeared at G'. 

The heat of the liquid, q, of a pound of steam at 100 degrees Fahrenheit 
is represented by OBNM, and the heat of vaporization (r) is MNG'F' , so 
that the total heat (q + r or H) is OBNG'F'. The total heat of wet steam 
is expressed by q+xr, where x is the quality or relative dryness. In 
the case of this adiabatic expansion, then, q is as before OBNM and 
xr is MNGF. It is obvious also that the lines NG and NG' have the 
same relation to each other as the areas under them, so that 



line NG area MNGF xr 



line NG' area MNG'F' 



NG 
NG' 



(70) 



showing that the quality of the steam at any point, G, on a constant 
temperature line (which for saturated steam is also a constant pressure 
line) is determined as in this case by the ratio of NG to NG', 



STEAM ENGINE TESTING 



267 



£ 




c/ 


T, and P 1 \ 


lE 




1 

a 
g 

B 






nA 




T.,and P., 


G 


v 





















P 


]p' 



conditions can be readily calculated from the data given in 
steam tables. 

Fig. 195 is an entropy-temperature diagram representing 
dry saturated steam which is expanded adiabatically from an 
initial temperature 
T x corresponding to 
a pressure Pi to a 
lower final tem- 
perature T 2 corre- 
sponding to a pres- 
sure P 2 . The other 
initial and final 
conditions of total 
heat (H) and en- 
tropy (0) are rep- 
resented by the 
same subscripts 1 
and 2 . The avail- 
able energy or the 
work that can be 
done by a perfect 
engine under these 

conditions is the area NCEG. It is now desired to obtain 
a simple equation expressing this available energy E rt in terms 
of total heat, absolute temperature and entropy. Explana- 
tions of the preceding figures should make it clear that 

H x =area OBNCEGF, 

H 2 =areaOBNG'F', 

E a =areas (OBNCEGF -fFGG'F') - OBNG'F', 

E =H 1 -H 2 +FGG'F / , 

th ere fore 

E a =R 1 -R 2 +(^ 2 -^ 1 )T 2 1 . ........ (71) 

An application of this equation will be made at once to 
determine the heat energy available from the adiabatic expan- 
sion of a pound of dry saturated steam at an initial pressure 

1 It should be observed that this form is for the case where the steam 
is initially dry and saturated. For the case of superheated steam a 
slightly different form is required which is given on page 272. 



Fig. 



Entropy 

-Practical Example of Adiabatic 
Expansion. 



268 



POWER PLANT TESTING 



of 165 pounds per square inch absolute to a final pressure of 
15 pounds per square inch absolute. 

Example. Pi =165 T 1 =. . . 

P2 = 15 T 2 =673.0 from steam tables. 1 

Hj =1193.6 from steam tables. 
H 2 =1146.9 from steam tables. 
<J>i =1.5605 from steam tables. 
<|>2 =i-7499 from steam tables. 
Substituting these values in equation (71), we have 
E a =ii 9 3.6-ii46.9 + (i. 7499-1. 5605)673.0 = 174.2 B.T.U. 

per pound of steam. 

The important condition assumed as the basis for the deter- 




P=° 'P X <P 1 % Entropy 

Fig. 196. — Entropy- temperature Diagram of Initially Wet Steam. 

mination of equation (71), that the steam is initially dry and 
saturated, must not be overlooked in its application. There 
are, therefore, two other cases to be considered: 

(1) When the steam is initially wet. 

(2) When the steam is initially superheated. 
Available Energy of Wet Steam. The case of initially wet 

steam is easily treated in the same way as dry and saturated 
steam. 

1 The values of the properties of steam given in the exercises are 
taken from Peabody's " Steam and Entropy Tables." (1909.) 



STEAM ENGINE TESTING 269 

Fig. 196 is an example of the case in hand. At the initial pres- 
sure Pi, the total heat of a pound of wet steam (q : +Xiri) is repre- 
sented in this diagram by the area OBNCE"^. The initial quality 

CE" 

of the steam (x{) is represented by the ratio of the lines -. 

CE 

The available energy from adiabatic expansion from the initial 

temperature Ti (corresponding to the pressure Pi) to the final 

temperature T 2 (corresponding to the pressure P 2 ) is the area 

NCE"G". If we call this available energy E aw , we have 

E aw = area OBNCEGF +FGGF' - OBNG'F' - G"E"EG, 

E f , w = H 1 -H 2 + (0 2 -^i)T 2 -(^i-^,)(T 1 -T 2 )/ 

E aw =H 1 -H 2 +(<j> 2 -c|, 1 )T 2 -^(i-x 1 )(T 1 -T 2 ).. . . (72) 

Example. Calculations of the heat energy from adia- 
batic expansion for the same conditions given in the preceding 
example on page 268, except that the steam is initially 5 per 
cent wet, are given below. 

Pi =165 lbs. abs. T L =825.9° F. 
P 2 = 15 lbs. abs. T 2 =673.o°F. 

Hi =1193.6 B.T.U. 

H 2 =1146.9 B.T.U. 

4>i=i-5 6o 5- 

4>2 =i-7499- 
r L =855.9 B.T.U. 

Xi=i.co-.c5 =.95. 

E a u, =II 93-6-ii46.9 + (i-7499-i-5 6o 5)673-°-^^- 

825.9 

X.o5(825. 9-673.0), 



Here 

because 



E BW = 166.3 


B.T.U. 






'In 


general terms, 


= 


xr 


■hO. 








&■ 




+ ?i 








4*- 


_x t r 

r, 


l + e v 








<h- 


-** 


-£ 



270 



POWER PLANT TESTING 



Specific Heat of Superheated Steam. In modern practice, 
superheated steam often enters our calculations, and a trouble- 
some modification of the entropy diagram results. The dif- 
ficulty arises because the specific heat of superheated steam is 
not very accurately known. The diagrams following are 
calculated for the specific heat determinations by Knoblauch 
and Jakob. 1 The specific heat of steam varies with the tem- 
perature and pressure as shown in Figs. 197 and 198, giving 















\ 




t 


\ 




















































\ 


\ 


















































\ 


\ 


\ 
















































\ 


\ 


\ 


\ 
















































\ 


} 




\ 
















































\ 




\ 


\ 












































K 






\ 


\ 












































, v 








V 


V 














































\ 






\ 


V 


S 








































/ 






\ 






\ 


\ 








































/ 






s 








\ 


\ 






































/ 




\ 




S 




\ 






\ 


V 








































s 




\ 










s 




















;A1 






















N 




\ 


^v 


*s 


< 
















Z-n 


'. - 
















































~ --}■'; 










, 










































-W1.-2 ■■ 
Lllli.li ■■ 






































































_ 




















. 85.2|.. 


















































-- 


8.4 '• 
14.2 " 





























































































































































































































a 

^ 3 SB 
O M „„ 

00 -d .56 

>% M 
g a 53 

* .50 

•4S 

.46 

.44 

.42 

200 250 300 350 400 450 500 550 600 650 700 750 

Temperature" I' 

Fig. 197. — Mean Values of Specific Heat (C p ) of Superheated Steam 

Integrated from Knoblauch and Jacob's Data. 

values of the mean and the true specific heat at constant pres- 
sure (C p ). 

True specific heat represents the ratio of the amount of 
heat to be added to a given weight of steam at some particular 
condition of temperature and pressure to raise the temperature 
one degree to that required to raise the temperature of water 
at maximum density one degree. The mean specific heat is 
almost invariably used in steam engine and turbine calculations. 

1 Zeit. Verein deutscher Ingenieure, Jan. 5, 1907. Values of mean 
specific heat are taken from Mechanical Engineer, July, 1907, and 
Professor A. M. Greene's paper in Proc. American Society of Mechanical 
Engineers, May, 1907. 



STEAM ENGINE TESTING 



271 



Entropy Diagram of Superheated Steam. The graphic 
representation of the heat added during the superheating of 
steam is easily shown with entropy-temperature diagrams. 
Fig. 199 shows a diagram similar to the one representing dry 
saturated steam with the added area EHJF to show the super- 



q0.70 



2 

^ 0.G0 







20 










1 


i\ \ 










16 












u/ 












12/ ' 












10/ \ 












s/ \ 




Pressu 
sq. c 


re in Kgr 
m. absoli 


i.per 
te. 


u 








^^ 


^^ 


































100° 



200 250 300 

Temperature = 0. 



Fig. 



-Values of the " True " Specific Heat of Superheated Steam. 

heating from the temperature, Ti corresponding to the pressure 
Pi to the temperature of the superheated steam, T s . The total 
heat in a pound of steam above the freezing point is now repre- 
sented by the area OBCEHJFO. For adiabatic expansion of 
superheated steam at the temperature T s and pressure Pi to a 
pressure P 2 the available energy is the area CEHKL. 



272 



POWER PLANT TESTING 



Too much calculation is involved in the construction of 

entropy diagrams to 
make a new diagram 
for every particular 
case from the proper- 
ties usually found in 
steam tables; but the 
construction of such 
diagrams should be 
understood. From 

the explanations that 
have preceded, the 
construction of all 
the lines except EH 
should be obvious. 
This line is obtained 
by calculating the en- 
tropy of superheated 
steam for various val- 
ues of temperature 
from the following 
well-known relations: 

, , fdQ f T °C p dT 

<f> a -<f>l = Cpm \log e ~ =2.3028 Cpm(log 10 (T s -log 10 T } ) V (73) 




Entropy 

— Entropy-temperature Diagram 
for Superheated Steam. 



and 



E to ,=H 1 -H 3 +C pm (T.-T 1 )-C rm .(T,'-T 2 ) 



(74) 



where E os is the available energy of the Rankine cycle for 
superheated steam and T g ' is calculated from the equation 
above where cj> s and (f> 2 ( = <f>i) are now both known quantities. 
£pm ^ s ^ e mean value taken from the curves in Fig. 197 for the 
temperature T s , and C' pm for T/. 

Approximate Steam Consumption Calculated from an Indi- 
cator Diagram. It is often very convenient to be able to calculate 
the approximate steam consumption of a steam engine from the 
data obtainable from an indicator card, the size of the piston, 



STEAM ENGINE TESTING 273 

the stroke, and the speed. Using a double-acting engine, the 
following symbols * may be used: 

p =mean effective pressure, pounds per square inch from 
indicator diagram. 

1 = length of the stroke of the engine in feet. 

a =area of the piston in square inches. 

b =percentage of clearance to the length of the stroke. 

c ^percentage of stroke at any point in the expansion line. 2 

n = number of revolutions per minute; and 120 n = number of 
strokes per hour. 

w =weight of a cubic foot of steam having a pressure as shown 
by the indicator diagram corresponding to that at the 
point in the expansion line selected for c, pounds, 
w' =weight of a cubic foot of steam corresponding to the pres- 
sure at the end of compression, pounds. 

la(b +c) 

Then the number of cubic feet per stroke = — in 

144(100) 

the clearance and piston displacement volumes (at c). 

Weight of steam per stroke, pounds = -. ^. (75) 

fa r ' r 144(100) Wvjy 

Volume of the clearance, cubic feet — 



[44(100) 

Weight of steam in clearance, pounds remaining in the 

r a law'(b ) 

cylinder = -. r . 

144(100) 

Approximate net weight of steam used per stroke 
law(b+c) law'(c) la 



[0. 



+c)w— cw' . (76) 



144(100) 144(100) i4,4oo| 

Approximate weight of steam from diagram per hour 
120 nlal 



14,400 



(b+c)w-cw' . . . . (77) 



1 Compare with Power, September, 1893. 

2 In other words this is the percentage of the entire stroke which 
has been swept through by the piston corresponding to the point in 
the expansion curve selected for measurements. It is preferable, how- 
ever, to take this point not very far from the point of cut-off, since 
the assumption must be made that the product of pressure times volume 
in the expansion curve is constant, which is, of course, not accurate, and 
the error becomes greater as the expansion increases. 



274 POWER PLANT TESTING 

i 

Indicated horse power for a double acting engine 

_ 2plan 
~33>ooo' 



(78) 



Steam consumption per indicated horse power is (77) divided 
by (78) or 



*=^^f(b+c)w-cw , l 



(79) 



The difference between the theoretical steam consumption 
calculated by the formula and the actual consumption as 
determined by tests represents steam " not accounted for by 
the indicator," due to cylinder condensation, leakage through 

ports, radiation, 
700 1 I I I I . I I I I I I — p-r-n — r-|-| — 1 ' i /f I 1 1 1 I e t c - If the steam 

supplied to the 
engine is very wet, 
corrections for this 
moisture should be 
made in the value 
of w. 

Willans Law. 
One of the most 
serviceable checks 
that can be applied 
to engine tests is 
plotting the Willans 
line of total steam 
consumption per 
hour. Curve sheets 
illustrating this as 
plotted from ac- 
tual tests by Bar- 
raclough & Marks 1 
are shown in Fig. 
200. It will be observed that the points representing the 
weight of steam used per hour when plotted for the horse 
power corresponding are on a straight line. In other words 
Willans law is usually stated thus: " With a fixed cut-off 





\F? 




j£ 




/^ 




7 




7 








7 




_y _j 




S 7* 




* y 




S 


~K 


7 B 




7 Z 


7 


-*£ S 


^ 


S 7- 




7 f + ' 




/r s 


y 7 


S 


y ^r 


^ y 




7 


/* 


J* 






^ ^ >c 




J. A 


1 


y. 




, 




' 




^ ^ 




* s 












ct 7 

















10 20 30 

Indicated Horse Power 

Fig. 200. — " Willans " Lines for an Engine with 
a Throttling Governor. 



Proceedings Institution of Civil Engineers, vol. 



20, page 323. 



STEAM ENGINE TESTING 275 

and a throttling governor the total steam used by the engine per 
hour at different loads can be represented by a straight line upon 
a mean effective pressure base or upon a horse-power base." It 
will be shown also in the following paragraphs how, theoretically, 
this relation holds for an engine operating at a fixed cut-off and 
with a throttling governor and that the steam consumption per 
hour is proportional to the mean effective pressure and also to 
the horse power developed. 

If we assume that the expansion curve is hyperbolic, which 
is usually near the truth, then the mean " forward " pressure 
given by an indicator diagram is x 

I ^), (80 

where pi is the initial pressure of the steam and r is the ratio 
of expansion. With a throttling governor r is of course constant. 
The terms in the parentheses can then be represented by a 
constant c and the mean forward pressure p/ then can be written 
as pic. Volume of steam used per hour for a double-acting 
engine can be expressed in cubic feet as 

120 (nV), (8i) 

where n is the number of revolutions per minute and V is the 
volume of steam admitted to the cylinder per stroke. Now if 
we use the symbol Vi for the specific volume, that is, the volume 
in cubic feet of a pound of steam at the pressure pi, and assum- 
ing for a small range of pressures that piVi =a constant k, then 
we can write, if W is the weight of steam used per hour in 
pounds, 

w=i 2o i nV) = i2o(nVp 1 ) 

Vi k v 

Now with a throttling governor and constant cut-off all these 
quantities are constant except pi, and writing a constant z 

for the term — ; we have W=zpi, but it was shown above 

k 

that the mean forward pressure p/=cpi, so that 

W=z^- f (83) 

1 Compare with Perry's " Steam Engine," page 2S6. 



276 POWER PLANT TESTING 

So that the curve -representing this equation is a straight line 
and passes through the origin of co-ordinates. If, however, we 
use the mean effective pressure instead of the mean forward 
pressure, then 

M.E.P.= P/ -p 6 , (84) 

where p& is the mean " back " or exhaust pressure. In these 
last terms then 

W=|(M.E.P.+p fe ) (85) 

This last equation may be stated as W = a constant XM.E.P. + 
another constant which, when plotted to a scale of mean effective 
pressure for abscissa and weight of steam used per hour for 
ordinates, is also a straight line, intersecting the axis of ordinates 
above the origin at a distance corresponding to the steam con- 
sumption per hour at no lead. 

Since the indicated horse power (I.H.P.) is proportional 
to mean effective pressure, a straight line will result when the 
steam consumption and indicated horse power are plotted; and 
the same holds true also when steam consumption is plotted 
with brake horse power (B.H.P.) instead of indicated horse 
power. 

Curves Showing Results of Tests Graphically. One of the 
best checks of an engine test is to plot the principal observations 
graphically as the test proceeds. This is particularly important 
as regards the total weight of steam used per hour. For a 
series of tests each made with a different load the points plotted 
with horse power (either indicated or brake) as abscissas and 
total steam per hour as ordinates should lie along a straight 
line, known as the Willans line (see page 274). This statement 
applies accurately only for engines operating with a throttling 
governor at, of course, constant speed; but is generally 
applicable to steam turbine tests, irrespective of the type of 
governor. 

Steam Engine Lubricators. The proper oiling of an engine 
is most important. The operation of nearly all types of lubri- 
cating devices is easily understood, particularly when operated 
by the gravity of the oil or by a pump. Another type of lubri- 
cator for cylinder lubrication which is operated by the weight 



STEAM ENGINE TESTING 



277 



of a column of condensed steam is shown in Fig. 201. The pipe 
C, in which the condensed steam accumulates, must be made at 
least 2 feet long to give a sufficient head or pressure to feed 
the oil. The oil reservoir is in the cylindrical vessel below the 
condenser pipe. This is filled with oil through an opening in 
the top as the water which has accumulated in the apparatus 
is drained through the cock D. Water from the condenser 




Fig. 201. — Engine Cylinder Lubri- 
cator Operated by Pressure of 
Column of Condensed Steam. 



Fig. 202. — " Detroit " Cylinder 
Lubricator. 



pipe C is carried down to the bottom of the oil reservoir by 
the pipe shown in dotted lines on the left-hand side. Oil, 
being lighter than the water, remains in the upper part of the 
reservoir and is forced down through the pipe on the right- 
hand side and through the needle-valve I by which the flow 
of oil can be regulated so that as small an amount as one drop 
in two or three minutes passes into the steam pipe at H to mix 
with the steam going to the engine cylinder. Through the 



278 POWER PLANT TESTING 

gage glass S the number of drops passing through can be observed. 
Another gage glass L on the side of the reservoir shows the 
relative amounts of oil and water. When an engine is not 
operating all oil cups and lubricators should be carefully closed. 

The feed of oil from this lubricator is stopped by closing the 
valves V and F. A valve is usually provided on the bulb 
B, which should be closed when draining from D, so that the 
water in the condenser pipe C will not be lost, and thus prevent 
the operation of the apparatus till a sufficient amount of 
condensed steam has accumulated to produce the pressure 
necessary to force the oil into the steam pipe. 

A slight modification of the lubricator described is illustrated 
in Fig. 202. The condensed steam is brought to the bottom of 
the reservoir through the pipe P, which is open at its lower 
end. On the other hand, the pipe S is open at the top and the 
oil is forced by the pressure due to the head of water in the 
pipe above (not shown) through the gage glass on the left- 
hand side, then through the horizontal pipe T to which is 
attached the valve and nipple connected to the steam pipe 
supplying the engine. In this figure at the top of the reservoir 
a plug with a nicely finished handle is shown, which is to be 
removed for filling with oil. 



CHAPTER XII 
TESTING STEAM TURBINES AND TURBINE GENERATORS 

Testing Steam Turbines. 1 In every power plant the means 
should be available for making tests of the steam equipment 
to determine the steam consumption. Usually tests are made 
to determine how nearly the performance of a turbine approaches 
the conditions for which it was designed. The results obtained 
from tests of a turbine are to show usually the steam consump- 
tion required to develop a unit of power in a unit of time, as, 
for example, a horse power hour or a kilowatt hour. 

In such tests a number of observations must be made regard- 
ing the condition of the steam in the passage through the tur- 
bine and of the performance of the turbine as a machine. To 
get a good idea of what these observations mean, it may be 
profitable to follow the steam as it passes through the turbine. 
The steam comes from the boilers through the main steam 
pipe and the valves of the turbine to the nozzles or stationary 
blades as the case may be. It then passes through the blades 
and finally escapes through the exhaust pipe to the condenser. 
It is preferable to have a surface condenser for tests, so that the 
exhaust steam can be weighed. The weighing is preferably 
done in large tanks mounted on platform scales. 

Methods for Testing. The important observations to be 
made in steam turbine tests are : 

i . Pressure of the steam supplied to the turbine. 

1 Tests of the turbines alone in a modern station may be only a 
rough indication of the over-all economy of the plant. Recently steam 
turbines were installed in a large power plant where they replaced steam 
engines of an excellent make. Tests of the turbines and of the engines 
made without considering the losses in the rest of the plant showed 
very little gain in efficiency by this change, although it was found that 
the fuel consumption was reduced twenty per cent. 

Parts of this chapter and the chapter following are taken from the 
author's work on " The Steam Turbine," 

279 



280 POWER PLANT TESTING, 

2. Speed of rotation of the turbine shaft, usually taken in 
revolutions per minute. 

3. Measurement of power with a Prony or a water brake, 
if the power at the turbine shaft is desired; or with electrical 
instruments (ammeters, voltmeters, and wattmeters), if the 
power is measured by the output of an electric generator. 

4. Weight, or measurement by volume, of the condensed 
steam discharged from the condenser. Unless a surface con- 
denser is used it is very difficult to obtain the amount of steam 
used by the turbine. All leakages from pipes, pumps, and 
valves, which are a part of the steam which has gone through 
the turbine, must be added to the weight of the condensed 
steam. The accuracy of a test often depends a great deal 
on how accurately leaks have been provided against, or 
measured when they occur. 

5. Temperature of the steam as it enters the turbine. If the 
temperature is higher than that due to the pressure of the 
saturated steam given in steam tables, the steam is superheated : 
if, however, the temperature is not higher the steam may be wet, 
and a calorimeter must be attached as near the turbine steam 
chest as possible. 1 

All gages, electrical instruments, and thermometers should 
be carefully calibrated before and after each test, so that observa- 
tions can be corrected for any errors. The zero readings of 
Prony and water brakes for measuring power should be carefully 
observed and corrected to eliminate the friction of the apparatus 
with no load. Unless all these precautions are taken the dif- 
ficulties in getting reliable tests of turbines are greatly increased. 
In all cases tests should be continued for several hours with 
absolutely constant conditions if the tests are to be of value. 

The most valuable test of a steam turbine or of a reciprocating 
steam engine is made when varying only the load ; that is, with 
pressures, superheat, and speed constant. When the steam 
consumption is then plotted against fractions of full load, a 

1 The most satisfactory tests of turbines are made with steam slightly 
superheated rather than wet. When steam is very wet (more than 
about 4 per cent moisture for ordinary pressures) the determination 
of the quality is difficult. There is also a danger that steam showing 
only a few degrees of superheat by the reading of the thermometer 
is actually wet. The high temperature is due in such cases to heating 
from eddies around the thermometer case or in steam pockets near it. 



TESTING STEAM TURBINES AND TURBINE GENERATORS 281 



water -rate curve is obtained. For such a curve a series of tests 
are needed, each for some fraction of full load; and in each 
separate test the power as well as all the other conditions must 
be held constant. 

Another important test of the performance of a steam 
turbine is made by varying both the speed and the power and 
keeping the other conditions constant. The observations of 
speed and power from such a test give a power parabola as 
illustrated in Fig. 203. 
This curve shows at 
what speed the tur- 
bine gives the greatest 
output. 

Tests may also be 
made with varying 
initial steam pressure, 
but keeping other con- 
ditions including ex- 
haust pressure and load 
constant. 

Calculations of the 
steam consumption and 
efficiency of turbines 
made by allowing for 
the different losses as 
calculated separately 
and then added to- 
gether as is often done 
to determine the losses 

in electrical apparatus are of very little value except when 
made by experienced designers. 1 

Commercial Testing. The methods used by the New York 
Edison Company in commercial tests of steam turbine-generator 
units may well be explained briefly. 

During a test the load on the turbine unit is maintained as 
constant as possible by " remote control " of the turbine gov- 



.50 
f.45 


















l j 




".DO 
















k^ 


l^w 










^ 






/ 


V 




a! 




g, 


400 


&35 

M.30 










vk; 






2\ 























|| 




M 


300 


















*i ^ 
























!! 


















\ 








1! 








$ 26 










\ 








«j 
















V 
















^25 
1 24 


e <*^ 














¥ 


.. 


> a 





















Yc 


x 








& 


















% 








§ 




|21 
J 20 






















■f 
























M 


-30 
























£18 



























Fig. 



203.- 



)0 800 1200 1600 2000 2100 
Speed E.P.M. 

-Results of Tests of a Turbine at 
Various Speeds. 



1 This method of calculation of steam consumption is explained in 
detail in "The Steam Turbine," by the author, pages 86-93. Steam con- 
sumption of a turbine can be predicted by calculations much more 
accurately than for a steam engine, 



282 POWER PLANT TESTING 

ernor by the switchboard operator. The maximum variation 
in load is to be held within 4 per cent above and below the mean. 
For some time previous to the test the turbine is run a little 
below the load required for the test, but at least ten minutes 
before the starting signal is given the test load must be on the 
machine. 

Three-phase electrical load is measured by the two-wattmeter 
method, 1 using Weston indicating wattmeters of the standard 
laboratory type. These instruments are calibrated at a well- 
known testing laboratory immediately before and after the 
test. Power factor is maintained substantially at unity and 
all electrical readings are taken at one-minute intervals. 

When the turbine is supplied with a surface condenser, the 
steam consumption, or water rate, is determined by weighing 
in a large tank supported on platform scales the condensed 
steam delivered from the condenser hot well. Above the 
tank on the scales a reservoir is provided which is large enough 
to hold the condensation accumulating between the weighings, 
which were made at intervals of five minutes. By using a 
loop connection for the gland water supply (of Westinghouse 
turbines) or the water from the step bearing (of Curtis turbines, 
using water for this bearing) the necessity for connecting the 
weighings for these amounts is avoided. 

Because the circulating water at the stations of this company 
is usually quite salty, any condenser leakage is detected by test- 
ing the condensed steam by the silver-nitrate test with a suitable 
color indicator. This color method is said to be a decided 
advantage over the usual method of weighing the leakage 
accumulating during a definite period when the condenser is 
idle and tested only with full vacuum. By taking samples 
of circulating water and condensed steam at the same time, 
it is possible to detect any change in the rate of condenser 
leakage. 

The water level in the hot well is maintained at practically 
a constant point by means of a float valve in the well, auto- 
matically controlling the speed and, therefore, the amount 
of the delivery of the hot-well pump. This device avoids the 

1 Cf . Kent's "Mechanical Engineer's Pocket-Book," 8th ed., page 
1396, or Foster's " Electrical Engineer's Pocket-Book," 4th ed., pages 51 
and 325. 



TESTING STEAM TURBINES AND TURBINE GENERATORS 283 

necessity for the difficult correction to be made in a test when 
the levels in the hot well are not the same at the beginning and 
end of a test. Temperatures and pressures of the admission 
steam are determined by mercury thermometers and pressure 
gages located near the main throttle valve of the turbine; the 
amount of superheat is determined by subtracting from the 
actual steam temperature after making thermometer connec- 
tions the temperature of saturated steam corresponding to the 
pressure at the point where the temperature is measured. All 
gages and thermometers are calibrated before and after the test. 

Vacuum is measured directly at the turbine exhaust by means 
of a mercury column with a barometer alongside for reducing 
the vacuum to standard barometer conditions (30 inches). By 
this latter arrangement the necessity for temperature connec- 
tions between the two mercury columns not at the same place 
is avoided. 

It has sometimes happened that split condenser tubes have 
caused a leakage of steam which was extremely difficult to 
measure. Cases are reported where the split opened up only 
when the condenser was heated with a large volume of steam. 
On this account it is preferable not to use a leaky condenser 
for accurate tests; in other words, the condenser should be thor- 
oughly repaired before tests are made. The effect of split 
tubes causing an irregular amount of leakage is usually shown 
in tests by inconsistent results in the weight of condensed steam. 
In that case the leakage will be greatest with largest flow of 
steam through the condenser and it will be observed, for an 
engine operating with a throttling governor or with a steam 
turbine, that when the " Willans line " page 274, is drawn to 
check the tests that it will be curved instead of straight. It 
should be noted, however, that a curved " Willans line " does 
not necessarily indicate this phenomenon in condenser leakage, 
as the irregularity may be due to faulty design of the engine 1 
or turbine. Tests of condensers for leakage should be run 
long enough so that the quantity of water coming through 
can be determined with accuracy. 2 Usually a leakage test 
run for less than an hour or two is of no use at all. 

1 The "Willans" line for a reciprocating engine operating with an 
automatic cut-off governor is usually a curve slightly concave upward. 

2 To determine accurately the weight of condensed steam the air- 



284 POWER PLANT TESTING, 

When the method of determining the weight, of condensed 
steam by weighing the boiler feed-water is used the chances of 
error are very great and every possible precaution to insure 
accuracy must be observed. In the first place valves no matter 
how good should not be relied on to prevent the passage of 
steam through them. For this reason careful engineers insist 
on disconnecting from the line of steam piping between the 
boilers and the engine or turbine tested all other piping con- 
nected to it, and then blanking off with flanges all the sections 
disconnected. If flanged pipe fittings have been used in the 
pipe lines, blanking off sections in the various pipes is very 
easily accomplished by disconnecting the flanges and inserting 
a thin iron or copper plate with holes around the edge to fit 
the bolt-holes in the flanges. The plate is then easily bolted 
in place. Another important precaution to observe is that the 
outlets of all drain or drip pipes and of all blow-off valves must 
be visible. It is equally important that all the piping between 
the boiler feed-pumps and the boilers is exposed with all branches 
blanked off or plugged. Boiler leakage should be determined 
before and after each test with preferably the pipe supplying 
the turbine blanked off at the throttle valve, although if the 
throttle valve is reasonably tight the precaution of blanking 
off this valve is not considered so important as the others men- 
tioned. In tests for boiler leakage the required steam pressure 
must be maintained on both the piping and the boilers. Measur- 
ing feed-water with water meters should not be thought of 
unless only approximate results are expected, and in that case 
such an arrangement is only allowable if the temperature of 
the boiler feed is not over 80 to 90 degrees Fahrenheit for most 
meters, and a by-pass at the meter is provided, so that at fre- 
quent intervals the meter can be calibrated by actual weighing 
of the flow through it, with the rate of flow and temperature 
of the water the same as in the tests. Boiler leakage is often 
as much as from ten to fifteen per cent of the. weight of feed- 
water, and in some reliable tests a still greater leakage has been 
observed. 

pump, piping, and tanks must be free from leaks, and. the condenser 
and pump should be so arranged with respect to each other that the 
condensed steam will flow in a continuous stream to the pump and 
into the tanks. 



TESTING STEAM TURBINES AND TURBINE GENERATORS 285 

Steam Consumption Determined by a " Heat Balance " 
Method. There is still another method sometimes used for 
determining the steam consumption of engines and turbines 
operated with jet condensers or condensers of a similar type 
where the cooling water and condensed steam are mixed and dis- 
charged together from the condenser. This method is based on 
the measurement of the amount of heat absorbed by the cooling 
water from the condensed steam. The weight w c and temper- 
ature of the cooling water leaving the condenser t 2 , the quality 
of the exhaust steam x and the temperature of the mixture of 
condensed steam and cooling water t" are determined as accu- 
rately as possible and from these data the weight of condensed 
steam w s is of course readily calculated by a simple algebraic 
equation as follows: 

w c (t 2 -32)+w s (q+xr) = (w c +w s )(t"- 3 2) . . (86) 

where q and r are respectively the heat of the liquid and the 
heat of vaporization corresponding to the temperature of the 
exhaust steam. In this equation " heat contents " are measured 
for each term from 32 degrees F. The method is, however, 
unreliable, and at best can be depended on for only very approx- 
imate results. The reason for this inaccuracy is the difficulty of 
measuring, especially in large plants, the quantity of cooling 
water and the true average temperature of a large volume of 
water flowing in a pipe or channel. It is found usually that the 
temperature of the water discharged from the condenser will 
vary from one side of the pipe to the other, and small errors in 
the determination of this temperature, because the rise in tem- 
perature is small, will make large discrepancies in the calculated 
weight of condensed steam. 

Stage pressures should be observed and recorded when tests 
are made of steam turbines having a series of pressure stages. 
These data are often extremely useful, both for checking the 
weight of condensed steam if the turbine is of the nozzle type * 

1 Usually the nozzles discharging the steam into the second stage 
of the turbine are always open, so that the total area is always constant. 
If, therefore, the areas of the smallest sections of these nozzles are 
measured and the pressure is observed in the first stage, the weight 
can be calculated with a considerable degree of accuracy by using the 
formula for the flow of steam on page 148. 



286 POWER PLANT TESTING ^ 

and also for showing any abnormal conditions in the several 
stages. 

Results calculated on a basis of kilowatts output should 
be net; that is, the power required for excitation should be 
subtracted from the generator output. If, however, the gen- 
erator is self-exciting the net output can be measured directly 
at the terminals of the machine. 

"Guarantee" tests of steam engines and turbines should be 
made under conditions as nearly as possible the same as that 
for which the turbine was designed. Different machines will 
have different correction factors for varying conditions of 
pressure, superheat, vacuum, etc., so that water rates cor- 
rected for large variations are always likely to be more or less 
inaccurate. This is particularly true in respect to vacuum 
corrections. Some turbines will give a very good efficiency 
with a low vacuum, but at a high vacuum because of an insuf- 
ficiently large steam space the efficiency will be low. 

HEAT UNIT BASIS OF EFFICIENCY 

A thermal efficiency can be calculated readily by deter- 
mining what percentage the heat equivalent of the work is of 
the heat " used by the turbine," assumed to be the difference 
between the total heat in the steam at the initial conditions 
and the heat of the liquid in the condensed steam at the 
temperature of the exhaust. 

By this method the full load test of a Westinghouse-Parsons 
turbine reported by F. P. Sheldon & Co., will be calculated from 
the data given in an official report. 

In order to make the results of such calculations of steam 
turbine tests comparable with the usual heat unit computa- 
tions of reciprocating steam engine tests the results are often 
expressed in terms of indicated or " internal " horse power. 
It was assumed the mechanical efficiency of a reciprocating 
engine of about the same capacity at this load was about 
93-3 per cent. 



TESTING STEAM TURBINES AND TURBINE GENERATORS 287 

THERMAL EFFICIENCY OF A 400-KILOWATT STEAM TURBINE 

Brake horse power 660 

Corresponding indicated or "internal" horse power of a recip- 

660 

rocatmg engine = 708 

•933 

Total steam used per hour, pounds 9169 

Steam used per "internal" horse power per hour, pounds 12 .96 

Steam used per "internal" horse power per minute, pounds. ... 0.216 

Steam pressure, pounds per square inch, absolute 166 . 9 

Superheat, degrees Fahrenheit 2.9 

Vacuum, referred to 30 inches barometer, inches 28 .04 

-Temperature of condensed steam, degrees Fahrenheit (at .96 

pound per square inch absolute pressure) 100 

Total heat contents of one pound of dry saturated steam at 

the initial pressure, B.T.U 1 193 

Heat equivalent of superheat in one pound of steam, B.T.U. 

(C p from Fig. 197, page 270) 1 

Total heat contents of one pound of superheated steam, B.T.U. 1195 

Heat of liquid in condensed steam, B.T.U. 68 

Heat used in turbine per pound steam, B.T.U 1127 

Heat used in turbine per "internal" horse power per minute, 

B.T.U. (n27.2X0.216) 243 

Heat equivalent of one horse power per minute, B.T.U. =— : . 2 

778 
Thermal efficiency, per cent (42.42 h- 243.5) J 7 

CALCULATION OF EFFICIENCY (SHAFT AND BUCKET) OF A 
STEAM TURBINE GENERATOR COMPARED WITH THE 
RANKINE OR CLAUSIUS CYCLE. 

1. " Electrical" kilowatts. 

2. R.P.M. 

3. Steam per hour (corrected for moisture). 

4. Water rate per " electrical " kilowatt, pounds per hour. (3) -f- (1) 

5. PR, loss in generator, kilowatts. 

6. Rotation loss of generator alone, kilowatts. 

7. Rotation loss of wheel and generator, kilowatts. 

8. "Shaft" kilowatts. (i) + ( 5 ) + (6) 

9. "Bucket" kilowatts. (i) + (s) + (7) 

10. Water rate per "shaft" kilowatt, pounds per hour. 

11. Water rate per "bucket" kilowatt, pounds per hour. 

12. Steam-chest pressure, pounds per square inch, absolute. 

13. Exhaust pressure, pounds per square inch absolute. 

14. Available energy, B.T.U. 

15. Theoretical water rate, pounds per kilowatt hour, B.T.U. = 

44200 
Avail. En. (14) 

16. " Shaft ' ' efficiency = (1 5) -=- (10) . 

17. " Bucket" efficiency = (15) -r(n). 

Notes. — For calculating rotation loss of a new design, stage pressures are of course 
used. 

Steam per hour is usually calculated from the area of the nozzles in the first stage if 
the governor is not operating. For a speed-torque test the flow of steam is constant and 



KW. for determining items (8) and (9) are read from this curve I KW. 



R.P.M. 



288 POWER PLANT TESTING 

In the case of steam turbines the net over -all efficiency or 

the heat equivalent of the "shaft" kilowatts compared with 
the available energy in the Rankine or Clausius cycle is the 
only one of any practical value to operating engineers. It 
shows the engineer how his engine is working in comparison 
with an assumed perfect engine. A comparison of different 
turbines on the basis of this net over-all or " shaft " efficiency 
is the most satisfactory way of considering their relative merits. 
Curves in Fig. 204 are given to compare the steam consump- 
tion of a standard turbine generator and a 4-cylinder compound 
reciprocating steam engine of the type used by the Interurban 
and Metropolitan Companies of New York, assuming both 

















































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u6y 


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rt 




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Fig. 204. — Comparative Water Rate Curves for Engines and Turbines. 



units operating under the same conditions. These curves 
illustrate the good overload economy or the turbine, showing 
that at 50 per cent overload the engine designed for equal 
work in the cylinders requires for the same output 43 per cent 
more steam than the turbine. 

These results are particularly interesting because the peak 
capacity of a station with a given equipment of boilers and 
auxiliaries is increased in proportion to the reduction of steam 
consumption at overload. For a given investment the turbine 
gives a much larger range of load and, moreover, affords the 
means by which the peak capacity of existing stations can be 
greatly increased. 

The speed output curve (Fig. 203) is very useful to engineers 
to determine if a turbine is running at its best speed. If the 



TESTING STEAM TURBINES AND TURBINE GENERATORS 289 

correspond' ng curves of steam consumption per kilowatt output 
(usually called water rate per kilowatt) and efficiency curves are 
calculated according to the form on page 287, a great deal of 
information is obtained about the operation and economy of a 
turbine. The torque line in Fig. 203 is always drawn straight, 
just as a " Willans line." A curve of total steam consump- 
tion is usually a straight line for the normal operating limits 
of a turbine, but usually becomes curved when a by-pass valve 
opens on overload, or when the turbine is over its capacity so 
that the pressures are not normal in the stages. 

The torque line shows why a turbine engine is not adaptable 
to automobiles. The starting torque of a small commercial 
turbine is not large, so that starting would be difficult with a 
small wheel, and reversing and speed reduction would be as 
difficult as with a gasoline engine. The reciprocating steam 
engine as well as the gasoline engine has, therefore, advantages 
over the steam turbine for this service. 

Method of Making Tests to Determine Wheel and Blade 
Rotation Losses of a Steam Turbine. The simplest method for 
making such a test, and the one commonly employed, is to 
attach an electric motor to the turbine shaft (sometimes in a 
direct-connected set the generator is used as a motor) and run 
it at a number of different speeds. In taking a series of speeds, 
no observations are made until conditions have become " steady," 
and the speed must be held constant for several minutes so that 
a number of readings can be taken on the electrical instruments 
measuring the input of the motor. The results give the rota- 
tion loss of the wheel and blades in steam as well as bearing 
friction and the rotation or " windage " and electrical losses 
of the motor. Then the turbine wheel is removed, leaving the 
packing at the generator end of the turbine on the shaft, and the 
motor is run alone. The power now measured is that required 
to overcome the rotation and electrical losses of the generator 
and the bearing friction. Curves of power and speed as vari- 
ables are plotted for each set of observations, and the disk 
and blade loss is determined by subtracting the ordinates of 
one curve from those of the other. It may be assumed with 
sufficient certainty that the weight of the turbine wheel itself 
would not alter the bearing losses to any considerable extent. 1 

1 It may be interesting to observe that since disk and blade friction 



290 POWER PLANT TESTING 

The important fact that all results given here are for disks 
and blades revolving in a stagnant medium must not be over- 
looked, and it must be not assumed that the results will be the 
same under actual operating conditions. It may be a coincidence • 
that the losses are the same in both cases. Under operating 
conditions, the spaces between the wheel blades are filled with 
steam flowing from the nozzle over the blades and then to the 
condenser. Now it has been shown by a series of experiments 
by Lasche of the Allgemeine Electricitat Gesellschaft (Berlin) 
that increasing the number of nozzles around the turbine wheel 
reduces the disk and blade rotation losses. These losses in the 
blades are very largely due to the fan action of the blades which 
start currents of steam just as a centrifugal fan does. In other 
words, this is what Stodola calls " ventilation." With steam 
flowing through the blades, this fan action is largely prevented 
and the losses are consequently reduced. Another reason why 
the disk and blade rotation losses should be less when the tur- 
bine is operating than they are in stagnant steam is that they 
are really friction losses, or a conversion of kinetic energy into 
heat, with the effect of either superheating or drying the steam. 
In a turbine with more than one stage a part of the heat energy 
gained as the result of the friction is converted in the next 
expansion into kinetic energy or velocity. It is usually assumed 
that about 1 5 per cent of the disk and blade losses are regained 
by reheating, and that therefore the actual friction losses in 
an operating turbine are about this amount smaller than in 
stagnant steam. In cases of full admission true blade friction 
disappears; and a proportionate reduction will also take place, 
according to the degree of admission, when it is partial. 

Investigation of wheel and blade friction losses by the author, 
using a modification of the method first suggested by Lasche of 
Berlin, did not show the reduction in these losses to be expected 
when determined under operating conditions. These results, 
however, cannot be considered conclusive, as the type of machine 
used was not well suited for the purpose, and only 25 per cent 
of the blades were filled with steam. It has been stated that 

is proportional to the density of the medium, the friction is therefore 
greater in air than in dry saturated steam at atmospheric pressure. 
This is shown by experiments published by Lewicki in Zeit. Verein 
deutscher Ingenieure, March 28, 1903. 



TESTING STEAM TURBINES AND TURBINE GENERATORS 291 

when a large quantity of steam passes into the casing through 
a suitable opening without passing through nozzles and escapes 
through the exhaust (without increasing the pressure), the 
disk and blade rotation losses are increased as much as 20 per 
cent. This apparently is an influence to counteract the effect 
of filling the blades. 

In all the analysis that has preceded there are so many 
uncertain variables entering that it is impossible to get agreement, 
although, apparently, we have a large amount of data from 
which to draw. It may be stated, however, that all in all, 
the best data on disk and blade friction seem to show that it is 
smaller and of less significance than the results of most investiga- 
tors would show. 

A little space should be given to Lasche's very interesting 
method. A turbine-generator set was used in which the num- 
ber of nozzles discharging into the turbine could be regulated 
and the output of the generator was observed for each setting 
of valves, and tests with varying loads were made at a number 
of different speeds. The turbine wheel was then removed from 
the shaft, and by running the generator as a motor the friction 
losses in the stuffing-box at the generator end of the turbine 
and in the bearings, as well as the windage loss of the generator, 
were determined. The resistance of the armature and brushes 
was also measured to calculate the heating (I 2 r) loss. The sum 
of these losses was calculated for a number of loads (kilowatts) , 
showing the electrical output at each speed. Another curve 
representing the power delivered to the shaft by the turbine 
was obtained by adding to the generator output for each set 
of nozzles open the corresponding generator losses (windage, 
heating, and bearing friction). The lower portions of both 
curves are practically straight lines, and by producing the latter 
curve to the horizontal axis, its intersection represents on the- 
scale of abscissas the disk and blade rotation losses of the turbine 
at the speed of the test and under actual operating conditions. 

By making a series of such tests at different speeds curves 
of rotation losses can be made. Although this method requires 
very careful experimenting, the same must be said of any other 
method of obtaining these losses. At least it must be admitted 
that by this method a number of uncertain factors to be con- 
sidered in the " stagnant steam " method are eliminated. 



292 POWER PLANT TESTING 

The curves obtained by this method are really the same 
as " Willans lines" (page 274), and might just as well be plotted 
for total "flow" of steam per hour as for nozzles open. In fact 
in turbines where there are no nozzles the ' ' flow ' ' of steam must 
be used. It is obvious that any load curve of brake horse 
power giving the total steam consumption can be used to deter- 
mine the rotation loss by producing the " flow " line to the 
axis on which the output is scaled. A good check on the 
results of such rotation loss tests is secured by observing whether 
the lines for the speeds near the rated speed cross each other 
at about the rated output. In a good design the speed-output 
curve will give nearly the same output at speeds considerably 
above or below the rating. 1 

The no load steam consumptions of 2000, 5000 and 9000 
kilowatt Curtis turbine generators are respectively about 14, 
12.5 and 8 per cent of that at full load. In other words these 
percentages are only from 1 to 2 per cent greater than the 
sum of the disk and blade rotation and generator windage losses. 
Generator windage loss is probably about equal to the sum 
of all the turbine losses. It is generally assumed that the no 
load steam consumption of a Parsons turbine (without the 
generator) is about 1 2 per cent of that at the normal maximum 
output. 

It is stated 2 that at no load the steam required for very large 
reciprocating engines and generators is probably in no case less 
than 1 5 per cent of that used at full load. 

Leakage Loss. The other important mechanical loss in a 
steam turbine is that due to the leakage of steam through the 
passages of the turbine without doing work. In impulse tur- 
bines of more than one stage this loss is chiefly caused by the 
leakage of steam between the shaft and the diaphragms. In a 
great many turbines no satisfactory packing is provided at 
these places and the loss is sometimes more than 10 per cent 
of the total anount of steam supplied to the turbine. In reac- 
tion turbines the loss is due to leakage through the radial clear- 
ance passages and is large or small in proportion to the size 

1 For a more detailed description and illustrative figures the reader 
is referred to the author's book on The Steam Turbine, pages 120-123. 

2 Kruesi, Proc. Am. Street and Interurban Railway Engineering 
Association, 1907. 



TESTING STEAM TURBINES AND TURBINE GENERATORS 293 

of these clearances. The loss is usually assumed to be about 5 
per cent in good Parsons turbines. 

Future improvements in the economy of all types of steam 
turbines will depend largely on the success of designers in reduc- 
ing these leakage losses. 

Analysis of Losses. The following table shows how the 
losses in a De Laval 200 -kilowatt turbine generator have been 
divided up by Stevens and Hobart : 

Nozzle losses 12 per cent 

Radiation losses and leakage 1 " 

Rotation losses due to the turbine wheel revolving in steam 4 ' ' 

Losses due to the steam traveling over the blades 9 ' ' " 

Bearing friction losses 1 " 

Losses in speed-reduction gearing 2 " 

Generator losses 4 " 

Losses due to residual kinetic energy in the steam passing 

to the condenser 8 " " 

Electrical output 59 " 

Total 100 

Electrical Output of Turbine Generators. Measurement of 
Direct Current. Careful engineers will not ordinarily use the 
instruments on the switchboard of a power station for measur- 
ing the electrical output of a generator, because, unless excep- 
tional precautions have been taken to avoid "stray " magnetic 
fields and the instruments have been calibrated in place under 
operating conditions with a sufficient interval of time between 
observations of current (amperes) at different loads so that the 
shunts of the ammeters will reach a constant temperature for 
the particular value of current flowing there may be con- 
siderable error in the observations. Switchboard voltmeters 
are usually satisfactory if they are carefully calibrated; but 
the shunts of the type of ammeters ordinarily used have 
approximately only 60 millivolts drop, so that the indicating 
part of the ammeter must be almost entirely a circuit of copper 
wire. It is for this reason that such instruments are likely 
to be affected considerably by varying room temperatures, and 
with some shunt arrangements they are susceptible to errors, 
also from variations in the value of the circuit itself. For 
accurate measurements, it is therefore best to use only the port- 
able types of indicating ammeters having shunts of 200 milli- 
volts 1 drop. In these latter instruments the indicating part 
'This value for the drop in shunts is an arbitrary value selected 



294 POWER PLANT TESTING 

is made up largely of resistance wires having practically no tem- 
perature coefficient. Portable voltmeters are also to be pre- 
ferred to those on the switchboards. 

Unless standard shunts of 2co millivolts drop as provided for 
good portable ammeters are used the influence of " stray " 
magnetic fields must be guarded against. When on the other 
hand switchboard instruments are used, such influences must 
be investigated and arrangements must be devised so that 
" stray " fields will not affect the measurements. The influence 
of very weak magnetic fields can be eliminated from the final 
results by turning the instruments between successive readings. 
Observations of current (amperes) made with the switchboard 
type of instruments, are also often in error due to thermo- 
electric effects producing a small electromotive force sufficient, 
however, to alter the readings of the millivoltmeter. The 
error due to this cause can be observed by reading the millivolt- 
meter at the close of the test immediately after the current has 
been shut off in the main circuit. It should be, of course, the 
object of the observer to take this reading before the shunts 
and leads have cooled appreciably. If there is an error due 
to this cause there will be a small position or negative deflection 
of the needle from the correct zero, which should be applied as a 
correction to all the observations of current. 

Measurement of Alternating Current. The same general 
precautions outlined above for direct -current instruments, must 
be observed in the use of those for alternating current. Although 
steady magnetic fields are not often a cause of much trouble, 
it happens often, particularly in the case of large generators, 
that there are large magnetic fields influencing the measuring 
instruments which have the same frequency as that of the cur- 
rent measured. To eliminate the effect of such " stray " fields 
shielded types of instruments shotild be used. Only with the 
most expert handling can accurate results be expected when 
unshielded instruments are used. For measuring large values 
of alternating current, instrument transformers are generally 
used. These should be of the precision type and should be sent 
to a standardizing laboratory before and after a series of tests 

by a number of makers of electrical instruments because it gives the 
best compensation of all the temperature errors. See General Electric 
Review, February, 191 1, 



TESTING STEAM TURBINES AND TURBINE GENERATORS 295 

to be calibrated, and a certificate of accuracy should be obtained. 
The transformers should be calibrated at as nearly as possible 
the values of the current to be measured in the tests. 

Whenever it is possible tests of generators should be made 
with a non-inductive load, water rheostats being usually the 
most satisfactory apparatus for providing such a load. At 
least tests should be made under conditions giving a low power- 
factor, so that there can be no error in the readings of the instru- 
ments due to phase displacements in the instrument trans- 
formers. With a purely non-inductive load the readings of the 
ammeters and the voltmeters can be used to check the watt- 
meters. Although the readings of the wattmeters should be 
taken as the correct value of the output the apparent power as 
indicated by the ammeters and voltmeters should agree with the 
wattmeter readings within one per cent. If a non-inductive load 
cannot be secured the switchboard ammeters and voltmeters 
will be satisfactory for readings to indicate whether or not the 
load on the circuits is properly balanced. Watt-hour meters 
are not usually satisfactory for the accuracy expected in most 
tests, and the use of these instruments should be generally 
avoided. It is only in the case where tests must be made 
under extremely variable service conditions, where it is difficult 
to obtain a true average from the readings of indicating instru- 
ments, that watt-hour meter, either for direct or for alternating 
current, may sometimes give more accurate results than the 
portable indicating types of instruments. Whenever watt- 
hour meters are used in tests they should be checked in place 
for a series of constant loads at the frequency, voltage/ etc. 
which are to be used in the test. 

Single-phase indicating instruments are to be preferred 
for measurements of polyphase current to the standard types 
of so-called polyphase instruments. The reason for this pref- 
erence is that the indications of a polyphase instrument are 
produced by two influences from separate phases of the current 
in such manner that a correction cannot be applied to obtain 
true values unless the division of the load is determined by the 
use of single-phase instruments. Obviously, then, if it is neces- 
sary to have single-phase instruments in the separate circuits, 
it is desirable to have them of the precision type, and polyphase 
instruments are not needed. 



CHAPTER XIII 

METHODS OF CORRECTING STEAM TURBINE AND ENGINE 
TESTS TO STANDARD CONDITIONS 

Standard Conditions for Turbine and Engine Tests. If tests 
of steam turbines and engines could be always made at some 
standard vacuum, superheat, and admission pressure, then 
turbines and engines of the same size and of the same type 
could be readily compared, and an engineer could determine 
without any calculations which of two turbines or engines was 
more economical for at least these standard conditions. But 
steam turbines and engines even of the same make are not 
often designed and operated at any standard conditions, so that 
a direct comparison of steam consumptions has usually no 
significance. 

It will be shown now how good comparisons of different 
tests can be made by a little calculation involving the reducing 
of the results obtained for varying conditions to assumed 
standard conditions. The method given here is that generally 
used by manufacturers for comparing different tests on the 
same turbine or engine (a " checking " process) or on different 
types to determine the relative performance. To illustrate the 
method by an application, a comparatively simple test will 
first be discussed. 

Practical Example. Corrections for Full Load Tests. The 
curve in Fig. 205 shows the steam consumption for varying 
loads obtained from tests of a 125-kilowatt steam turbine 
operating at 27.5 inches vacuum, 50 degrees Fahrenheit super- 
heat, and 175 pounds per square inch absolute admission pres- 
sure (at the nozzles) . It is desired to find the equivalent steam 
consumption at 28 inches vacuum, o degrees Fahrenheit super- 
heat, and 165 pounds per square inch absolute admission pres- 
sure for comparison with the "guarantee tests" (Fig. 206) of a 
steam engine of about the same capacity operating at the latter 

296 



METHODS OF CORRECTING TURBINE AND ENGINE TESTS 297 



conditions of vacuum, superheat, and pressure. The manu- 
facturers of the steam turbine have provided the curves in 
Figs. 207, 208, and 209, showing the change of economy with 




20 



10 



L60 



180 



:.'0i) 



60 80 100 120 110 

Output of Generator in Kilowatts 

Fig. 205. — Water Rate Curve of a Typical 125-Kilowatt Steam Turbine. 

(Generator Output.) 

varying vacuum, superheat, and pressure. With the help 
of these correction curves, the steam consumption of the tur- 
bine can be reduced to the conditions of the engine tests. Fig. 



•2 §35 

s«30 

















































\ 

\ 














































\ 












































' 


\ 










































\B 


» 


X 














































s s 
















































^ 
















































^c 














__. 


.-■ 


-'" 


















































































































A. Steam Consumption of Engine 






























of g 


tea 


nT 


urb 


ne. 

















gs* 



30 10 60 80 100 120 140 160 180 200 

Output of Generator in Kilowatts 

Fig. 206. — Comparative Water Rate Curves of a Reciprocating Steam 
Engine and a Steam Turbine. (Both with Standard Generators.) 

207 shows that between 27 and 28 inches vacuum a difference 
of 1 inch changes the steam consumption 1.0 pound. Fig. 

208 shows a change of 2.0 pounds per 100 degrees Fahrenheit 



298 



POWER PLANT TESTING 



superheat, and from Fig. 209 we observe a change of 5.0 pounds 
in the steam consumption for 100 pounds difference in admission 
pressure. Compared with the engine tests the steam turbine 
was operated at .5 inch lower vacuum, 50 degrees Fahrenheit 
higher superheat, and 10 pounds higher pressure. At the con- 

















































30 


























































































25 


























































































20 


























































































15 















































21 



Ti 



29 



Fig. 207. 



23 24 25 26 

Vacuum Inches of Mercury 
-Vacuum Correction Curve for a 125-Kilowatt Steam Turbine. 



ditions of the engine tests, then, the steam consumption of the 
steam turbine should be reduced . 5 pound to give the equivalent 
at 28 inches vacuum, but is increased 1.0 pound to correspond 
to o degrees Fahrenheit superheat, and .5 pound more to bring 
it to 165 pounds absolute admission pressure. The full load 




SO 100 120 140 

Superheat -Degs. Fahr. 

Fig. 208. — Superheat Correction Curve for a 125-Kilowatt Steam Turbine. 

steam consumption for the steam turbine at the conditions 
required for the comparison is, therefore, 24.5 — .5 + 1.0 +.5, or 
25.5 pounds. 1 

1 The corrected steam consumption is found to be nearly the same 
as that which the three correction curves show for the same conditions, 
that is, about 25.0 pounds. If there had been a difference of more 
than about 5 per cent between the corrected steam consumption and 



METHODS OF CORRECTING TURBINE AND ENGINE TESTS 2C9 

Persons who are not very familiar with the method of making 
these corrections will be liable to make mistakes by not knowing 
whether a correction is to be added or subtracted. A little 
thinking before writing down the result should, however, pre- 
vent such errors. When the performance at a given vacuum 
is to be corrected to a condition of higher vacuum, the correc- 
tion must be subtracted, because obviously the steam consumption 
is reduced by operating at a higher vacuum. When the steam 
consumption with superheated steam is to be determined in its 
equivalent of dry saturated steam (o degrees superheat) the 
correction must be added because with lower superheat there 
is less heat energy in the steam and consequently there is a 

















































a 1* 
.2 5 25 

SW20 














































































































































































as,, 

ft* 


























































































10 















































loo no 



120 



11)0 



200 



130 140 150 160 170 180 
Steam Pressure -Lbs. Per Sq. In. Abs. 

Fig. 209. — Pressure Correction Curve for a 125-Kilowatt Steam Turbine. 

larger consumption. Usual corrections for differences in 
admission pressure are not large; but it is well established 
that the economy is improved by increasing the pressure. 

Corrections for Fractional Loads. It is the general expe- 
rience of steam turbine manufacturers that full-load correction 
curves, if used by the following "ratio " or percentage method, 
can be used for correcting fractional or over loads. This state- 
ment applies at least without appreciable error from half to 
one and a half load, and is the only practicable method for 
quarter load as well. 1 Stated in a few words, it is assumed 
then that the steam consumption at fractional loads is changed 
by the same percentage as at full load for an inch of vacuum, 

that of the correction curves for the same conditions, the "ratio" 
method as explained on page 300 for fractional loads should have been 
used also for full load. 

1 A very exhaustive investigation of this has been made by T. Stevens 
and H. M. Hobart, which is reported in Engineering, March 2, 1906. 



300 



POWER PLANT TESTING 



a degree of superheat, or a pound pressure. It will now be 
shown how this method applies to the correction of the steam 
consumption of the turbine at fractional loads. Now accord- 
ing to the curve in Fig. 207, the steam consumption at 27.5 
inches (25.6 pounds) must obviously be multiplied by the ratio 1 

— — . of which the numerator is the steam consumption at 28 
25-6 

inches and the denominator at 27.5 inches, to get the equivalent 
consumption at 28 inches vacuum. This reasoning establishes 
the proper method for making corrections; that is, that the 
base for the percentage (denominator of the fraction) must be 
the steam consumption at the condition to which the correc- 
tion is to be applied. 2 Similarly the correction ratio to change 
the consumption at 50 degrees Fahrenheit superheat to o degrees 

2^0 
Fahrenheit is - • ' -, and to correct 175 pounds pressure to 165 



pounds the ratio is 



24.8 
24-3' 



Data and calculated results obtained 



by this method may then be tabulated as follows : 





Conditions 
of Test. 


Required 
Conditions. 


Correction 
Ratio. 


Percentage 
Correction. 




27-5 
5°- 

175- 


28 


165 


25.0 
25.6 
25-° 
24 . 
24.8 

24-3 


-2.34%* 
+ 4-i7% 

+ 2.06% 
+ 3-89% 


Superheat, degrees Fahrenheit 

Admission pressure, pounds 
absolute 











* Steps in the calculation are omitted in the table, thus -—- = .9766 or 97.66 per cent 

25.6 
making the correction 100 — 97.66, or 2.34 per cent. It may seem unreasonable to the 
reader that these percentages are calculated to three figures when the third figure of 
the values of steam consumption is doubtful. In practice, however, the ruling of the 
curve sheets must be much finer and to larger scale so that the curves can be read more 
accurately. 

1 Assuming that this short length of the curve may be taken for a 
straight line without appreciable error. 

2 In nearly all books touching this subject so important to the 
practical, consulting, or sales engineer, the alternative method of taking 
the steam consumption at the required conditions as the base for the 
percentage calculation is implied. By such a method percentage cor- 
rection curves derived from straight lines like Figs. 208 and 209 would 
be straight lines and, in application, give absurd results. Actually 
such percentage corrections will fall on curves. 



METHODS OF CORRECTING TURBINE AND ENGINE TESTS 301 

The signs + and — are used in the percentage column to 
indicate whether the correction will increase or decrease the 
steam consumption. " Net correction " is the algebraic sum 
of the quantities in the last column. 

The following table gives the results of applying the above 
" net correction " to fractional loads. 



\ Load 
31.3 kw. 


i Load 
62.5 kw. 


| Load 
93.8 kw. 


f Load 
125 kw. 


31.2 

+ 1.2 
3 2 -4 


26 .9 

4- 1.1 

28.0 


25.2 
+ I.O 
26 . 2 


24-5 
+ 1.0 

2 5-5 



S Load 
156.3 kw. 



Steam consumption from 

test (Fig. 205) 

Net correction + 3 . 89% 

Corrected steam consumption 



23.6 
+ 0.9 

24-5 



Curve B in Fig. 206 shows the corrected curve of steam con- 
sumption for the steam turbine as plotted from the above table. 
By thus combining, on the same curve sheet, curves A and B as 
in this figure, the points of better economy of the turbine are 
readily understood. 

Results of economy tests of the various turbines given on the 
preceding pages are of very little value for comparison when 
the steam consumptions or "water rates " are given for all sorts 
of conditions. With the assistance, however, of curves like 
those shown in Figs. 207, 208 and 209, if they are representative 
of the type and size of turbine tested, it is possible to make 
valuable comparisons between two or more different turbines. 
Some very recent data of Curtis and Westinghouse-Parsons 
turbines are given below, together with suitable corrections 
adopted by the manufacturers for similar machines. 

The following test of a Westinghouse-Parsons turbine, rated 
at 7500 kilowatts, was taken at Waterside Station No. 2 of the 
New York Edison Co., and a comparison is made with a test of 
a five-stage 9000 -kilowatt Curtis turbine at the Fisk Street 
Station of the Commonwealth Electric Company of Chicago. 
As no pressure correction is given for the Curtis machine, the 
New York Edison test is corrected to the pressure at which the 
other machine was operated (179 pounds per square inch gage). 
Approximately an average vacuum for the two tests is taken 
for the standard, and 100 degrees Fahrenheit superheat is used 
for comparing the superheats. These assumed standard con- 



302 



POWER PLANT TESTING 



7500 KILOWATT WESTINGHOUSE-PARSONS TURBINE, WATER- 
SIDE STATION NO. 2, NEW YORK EDISON COMPANY 
Tested September i, 1907 



Corrected 



Correction 
per cent.* 



Duration of test, hours 

Speed revolutions per minute 

Average steam pressure, pounds gage . . . 

Average vacuum, ins. (referred to 30 in. 
barom.) 

Average superheat, degrees Fahrenheit . . 

Average load on generator, kilowatts. . . . 

Steam consumption, pounds per kilo- 
watt-hour 

Net correction, per cent 

Corrected steam consumption, pounds 
per kilowatt-hour 



75° 
177-5 

27-3 

95-7 

9830.5 

i5-i5t 



79 



28.5 
100 



■3-30 
o. 29 



•3.80 



*The following corrections were given by the manufacturers and accepted by the pur- 
chaser as representative of this type and size of turbine : 

Pressure correction .1 per cent for 1 pound. -> 

Vacuum correction 3.5 per cent for 1 inch. I from Electric Journal, 

Superheat correction 7.0 per cent for 100 degrees Fahren- | November, 1907, page 658. 
heit. J 

t This is -j\ per cent better than the manufacturer's guarantee. 

9000 KILOWATT CURTIS TURBINE, FISK STREET STATION, 
COMMONWEALTH ELECTRIC COMPANY, CHICAGO. 



Tested in 



:9°7 







Corrected 
to 


Correction, 
per cent.* 












7 5° 
179 

29-55 
116 
8070. 

i3-o 






Average steam pressure, pounds gage . . 
Average vacuum, inches (referred to 3c 


179 

28.5 
IOO 


.0 

+ 12.39 
+ I.28 


Average superheat, degrees F 

Average load on generator, kilowatts. . . . 
Steam consumption, pounds per kilo- 










+ 1367 


Corrected steam consumption, pounds 




14.77 









* The following percentage corrections were used': 
Superheat corrections 8 per cent for 100 degrees Fahrenheit. 
Vacuum correction 8 per cent for 1 inch from c rve in Fig. 21c 
Pressure correction not given. 



E. Bulletin, 
No. 4531. 



METHODS OF CORRECTING TURBINE AND ENGINE TESTS 303 



ditions make the corrections for each turbine comparatively 
small. When two tests are to be compared, by far the more 
intelligent results are obtained if each is corrected to the average 
conditions of the two tests, rather than correcting one test 
to the conditions of the other. There is always a chance for 
various errors when large corrections must be made. 

These results show a difference of only .20 pound in the cor- 
rected steam consumption, so that for exactly the same con- 
ditions these two machines would probably give approximately 
the same economy. Each turbine is doubtless best for the 
special conditions for which it was designed. 

These results are equivalent to respectively 9.58 pounds and 
9.72 pounds per indicated horse power, assuming 97 per cent as 
the efficiency of the 
generator and 9 1 per 
cent as the mechani- 
cal efficiency of a 
large Corliss engine 
according to figures 
given by Stott. 1 

From experience 
with other similar 
turbines it seems 
as if the vacuum 
corrections given 
are too low for 
each turbine. The 
correction for the 
Curtis turbine was obtained from the curve in Fig. 210, 
as given between 27 and 28 inches, while it was used 
between 28.5 and 29.5 inches, where the curve of steam 
consumption most likely slopes somewhat, as shown by the 
dotted line in the figure, which was derived from the per- 
centage change of the theoretical steam consumption calculated 
from the available energy. The correction of 2.7 per cent 
per inch of vacuum for the Westinghouse-Parsons turbine is 
probably too low also, although the percentage correction 

1 Electric Journal, July, 1907. It is stated also in this article that the 
vacuum correction of a Westinghouse-Parsons turbine is 3.5 per cent 
per inch between 28 and 28.5 inches. Jude states that the vacuum cor- 
rection for Parsons turbines is 5 to 6 per cent. 



.2 » 

M 

o u 

-3 

































18 


























































1G 














































































s 


S N 
































N 






1~> 


























\ 
































10 































:« 



2± 



27 



Vacuum Inches of Mercury 
Fig. 210. — Typical Vacuum Correction Curve for 
a 5000-Kilowatt Impulse Turbine. 



304 



POWER PLANT TESTING 



would not be nearly as large as for the Curtis. If both of these 
corrections are too low, the effect of increasing them would 
be to increase the corrected steam consumption of the Curtis 
turbine and reduce that of the Westinghouse-Parsons. 

Tests of a 5000 -kilowatt Curtis and a 7 500 -kilowatt Westing- 
house-Parsons turbine are also recorded here for comparison. 
The two tests are corrected to the assumed standard conditions 
of 173.7 pounds gage pressure, 28 inches vacuum, and o degrees 
Fahrenheit superheat. For the test of the Curtis machine the 
same percentage corrections were used as for the 9000 -kilowatt 
turbine; and for the test of the Westinghouse turbine the 
vacuum correction is that given in the footnote at the middle 
of page 302 (3.5 per cent per inch), while the other percentage 
corrections are the same as in the preceding test of a similar 
machine. The Westinghouse turbine was operated with wet 
steam. In a test of a reciprocating engine the equivalent 
economy with dry steam is calculated by merely subtracting 
the percentage of moisture, but in a turbine test the correction 
is generally stated as being a little more than twice the percent- 
age of moisture. In other words, in a turbine test the moisture 
must be subtracted twice. The reason for this difference in 
the methods of correcting water rates of engines and turbines 
is the very large increase in the disk and blade rotation losses 
in wet steam 

5000-KILOWATT FIVE-STAGE CURTIS TURBINE, L STREET 

STATION, BOSTON EDISON COMPANY 

Tested January 29, 1907 







Corrected 
to 


Correction, 
per cent. 




3 
720 

173-7 

28.8 
142 
5 J 95 

*3-5 2 












Average steam pressure, pounds gage . . . 
Average vacuum in. (referred to 30 in. 


173-7 

28 
O 


O 


Average superheat, degrees Fahrenheit . . 
Average load on generators, kilowatts. . . . 
Steam consumption, pounds per kilo- 


+ 11.36 










+ 17-76 


Corrected steam consumption, pounds 




!5-9 2 









METHODS OF CORRECTING TURBINE AND ENGINE TESTS 305 



7500-KILOWATT WESTINGHOUSE-PARSONS TURBINE. INTER- 
BOROUGH RAPID TRANSIT COMPANY, NEW YORK 
Tested in 1907 







Corrected 
to. 


Correction, 
per cent. 




3 












Average steam pressure, pounds gage . . . 
Average vacuum, in. (referred to 30 in. 


149.7 

27.70 
3-° 
7135 

17.79 


173-7 

28 
O 


-2.4 

-I.05 
-6.0 


Average moisture, per cent 

Average load on generator, kilowatts. . . . 
Steam consumption, pounds per kilo- 










-9-45 


Corrected steam consumption, pounds 




16 . 10 









It is stated that the steam consumption of the Interborough 
Company's turbine is 15.87 pounds at full load and 15.54 pounds 
at 9000 kilowatts when the overload valve opens. The gen- 
erator connected to this turbine is rated at only 5500 kilowatts. 
With a generator more nearly the rating of the turbine it is 
probable still better results would be secured. 



CHAPTER XIV 
GAS AND OIL ENGINE AND PRODUCER TESTING 

The testing of internal combustion engines of the reciprocat- 
ing type operating with gas, gasoline, kerosene, and alcohol 
does not differ essentially in the important details from steam 
engine practice already explained in Chapter XI. Indicator 
diagrams must be utilized to show the inner workings in the 
engine cylinder, giving a record of the pressure, " timing " 
of the valves and ignition for the operation of the engine through 
a cycle. 1 

Brake horse power is measured with a Prony brake or any 
other type of dynamometer permitting the determination with 
facility of the power of the engine. If with a Prony brake or 
similar device (see page 122) then the brake horse power is 
expressed by the usual formula, 

B.H.P.= 2 -^ (87) 

33,ooo 

where 1 is the length of the brake-arm in feet, n is the number 
of revolutions per minute, and w is the net weight indicated 
by the scales on the brake. Similarly the indicated horse power 
is given by the Uoual formula for a single-acting steam engine 
(page 118) except that the number of explosions must be used 
in calculations instead of the number of revolutions, thus, 

I.H.P.= Pk*- (88) 

33,ooo 

1 In what is called usually a four-cycle engine there are four piston 
strokes — one each for suction, compression, expansion, and exhaust, 
corresponding to two revolutions of the crank shaft for a complete cycle, 
while in a so-called two-cycle engine, two strokes of the piston make a 
complete cycle — corresponding to one revolution of the crank-shaft. In 
the latter case suction and compression are combined in one stroke and 
expansion and exhaust in another. 

306 



GAS AND OIL ENGINE AND PRODUCER TESTING 307 

where p is the mean effective pressure in pounds per square inch 
measured from the indicator diagram, 1 is the length of the 
stroke in feet, a is the area of the piston in square inches, and 
n e is the number of explosions per minute, then 

B H P 

Mechanical Efficiency = ' ' ' . . . (89) 

Certain important precautions should be observed when 
taking indicator diagrams, so that a reasonable degree of accuracy 
may be expected from the results of tests. In the first place 
the connections between the indicator and the combustion 
chamber should be as short as possible. It is much more 
important that in an internal-combustion engine the volume by 
which the combustion chamber (clearance) is increased by the 
indicator connections should be small in comparison to the 
volume of the engine cylinder than in a steam engine; because 
by increasing the clearance volume, obviously, the pressure 
resulting from compression is reduced as well as the pressure 
due to the explosion. It is in this way that large indicators 
and indicator connections may cause a considerable reduction 
in the thermal efficiency of an engine, that is, reducing the 
efficiency of the transformation of heat energy into work. 

Tests of gas engines as made commercially have usually 
three objects in view: 

(1) Brake horse power. 

(2) Indicated horse power. 

(3) Gas or oil consumption per horse power per hour. 
Many types of gasoline engines, particularly those designed 

for the automobile service, operate at such high speeds that the 
indicated horse power cannot be obtained with accuracy. 
In many other kinds of engines classed in this group the mechan- 
ical efficiency is very low. It is for these reasons that such 
engines are rated by the useful or brake horse power instead 
of by the indicated horse power, as with steam engines. Brake 
horse power is therefore the prime criterion by which the per- 
formance of these engines is expressed. 

Ordinary types of steam engine indicators, moreover, are 
not very satisfactory for testing gas engines, and many engi- 
neers prefer to use one of the type shown in the accompanying 
illustration, Fig. 211. It differs essentially from steam engine 



308 POWER PLANT TESTING 

indicators of the same type in having in the lower part of the 
main " barrel," a cylinder of smaller diameter than the one 
just above it, containing the spring. This smaller cylinder 
takes a piston of only half the area of the standard size. By 
this means the scale of the spring ordinarily used is doubled 
and the shock on the small rods and levers of the pencil motion 




-Crosby Gas Engine Indicator. 

is only half as great, thus making the liability to breakage and 
the cost of repairs for such indicators very much less than when 
a piston of the standard size is used. 

Measurement of the Fuel Used. For tests of gas engines 
the gas used is usually measured by means of a gas meter. 
A so-called " wet " meter (page 143) is always to be preferred, 
but if a carefully calibrated dry meter is used very good results 
can be obtained and it is accurate enough for commercial 
tests. For gasoline, kerosene, and other oil engines the amount 
of fuel used is preferably determined by direct weighing. The 



GAS AND OIL ENGINE AND PRODUCER TESTING 309 

author has found the automatic indicating scales of the pen- 
dulum type 1 now generally used by grocers and meat dealers 
to be most satisfactory. By this means the weight of the oil 
remaining in the " supply " vessel can be observed regularly 
throughout a test just as with a gas meter, so that irregularities 
in operation can be immediately observed. The vessel contain- 
ing the oil used by the engine when placed on a scales must be 
connected to the carbureter or the pump, as the case may be, 
with a very flexible metallic tube made without rubber inser- 
tion. 2 If an indicating scales is not available a very small 
platform or grocers beam scales can be used satisfactorily, 
although if the weight of fuel oil is desired at regular intervals 
throughout a test some little time is required to balance the 
poise. 

Another method very commonly used, however, is to use 
a cylinder vessel of small diameter provided with a gage glass 
in which the level of the liquid can be observed. Such a vessel 
can be calibrated to determine the weight or volume of oil 
per inch of height measured on the gage glass. 

Observations taken for a test of a gas or oil engine are in 
general much more uniform than the corresponding data taken 
in a steam engine trial. For this reason gas engine tests in 
particular can be made of much shorter duration than upon 
a steam engine for the same degree of accuracy. 

For both gas and oil engines the points plotted on a scale 
of brake horse power for abscissas and fuel used per unit of 
time for ordinates will fall along a straight line, similar and resem- 
bling the Willans line for steam engines and steam turbines 
(see page 274). A typical set of curves of the results of a test 
of a gas engine is shown in Fig. 212. Brake horse power is 
taken for the abscissas, as should always be done for gas and 
oil engine tests and gas used per hour, to its corresponding scale 
of ordinates, is given by the top curve. Other curves show the 
gas used per brake horse power per hour and per indicated 

1 Very satisfactory scales for this purpose are made by the Toledo 
Scale Co. of Toledo, Ohio. -Similar scales of the spring type are not 
recommended, because necessarily some of the vibrations of the engine 
will be transmitted to the scales and the indications of the pointer will 
not be as accurate as they should be. 

2 Tubes of this kind are made by the U. S. Metallic Tube Co. of Los 
Angeles, Cal. 



310 



POWER PLANT TESTING 



horse power per hour, the indicated horse power, the mechan- 
ical efficiency, the number of explosions per minute, the revo- 
lutions per minute and the thermal efficiency (heat equivalent 
of the indicated horse power divided by heat supplied). 

The following paragraphs and tabular forms are taken 
from the " Rules for Conducting Tests of Gas or Oil Engines " as 

adopted by the American 
Society of Mechanical En- 
gineers. 1 

Duration of Test. The 
duration of a test should 
depend largely upon its 
character and the objects 
in view, and in any case 
the test should be continued 
until the successive readings 
of the rates at which the oil 
or gas is consumed, taken 
at, say, half -hourly intervals, 
become uniform and thus 
verify each othei. If the 
object is to determine the 
working economy, and the 
period of time during which 
the engine is usually in 
motion is some part of 
twenty-four hours, the dura- 
tion of the test should be 
fixed for this number of 
hours. If the engine is one 
using coal for generating 
the gas, the test should cover a long enough period of time 
to determine with accuracy the coal used in the gas producer; 
such a test should be of at least twenty-four hours' duration, 
and in most cases it should extend over several days. 

Measurement of Fuel. If the fuel used is coal furnished to a 
gas producer, the same methods apply for determining the con- 
sumption as are used in steam boiler tests. (See pages 21C-21 7.) 

1 Transactions American Society of Mechanical Engineers. Vol. 24, 
pages 775-79°, 




Brake 

Fig. 212. — Typical Economy, Speed, 
Horse Power and Efficiency Curves 
of a Five Horse Power Gas Engine. 



GAS AND OIL ENGINE AND PRODUCER TESTING 311 

If the fuel used be gas, the only practical method of measur- 
ing is the use of a meter through which the gas is passed. Gas 
bags should be placed between the meter and the engine to 
diminish the variations of pressure, and these should be of a 
size proportionate to the quantity used. Where a meter is 
employed to measure the air used by an engine, a receiver with 
a flexible diaphragm should be placed between the engine and 
the meter. The temperature and pressure of the gas should be 
measured, as also the barometric pressure and temperature of 
the atmosphere. 

Data and Results of test of Gas or Oil Engine 
Standard Form 

i. Made by of 

on engine located at 

to determine 

2. Date of trial 

3. Type of engine, whether oil or gas 

4. Class of engine (mill, marine, motor, for vehicle, pumping or 

other) 

5. Number of revolutions for one cycle and class of cycle 

6. Method of ignition 

7. Name of builders 

8. Gas or oil used 

(a) Specific gravity 

(b) Flashing point, deg. F. 1 (open or closed vessel) 

(c) Burning point, deg. F. . . 

9. Dimensions of engine 

(a) Class of cylinder (working or for compressing the charge) 

(b) Vertical or horizontal 

(c) Single or double acting 

(d) Cylinder dimensions 

Bore, ins 

Stroke, ft*. 

Diameter piston rod, ins 

Diameter tail rod, ins 

(<?) Compression space or clearance in per cent of volume dis- 
placed by piston per stroke 

Head end 

Crank end 

Average 

1 The flashing- point of fuel oils lighter than about 70 Baume (0.70 specific gravity) 
is at "room" temperatures so that no test is needed. The flashing-point of heavier oils 
is usually made by heating the oil in a vessel closed at the top with a glass plate in which 
there are openings for the insertion of a thermometer and for testing with a lighted match 
or taper. The flash-point is the temperature observed when the vapor on the surface of 
the oil first flashes. If the flashing- point is determined in an open vessel the value is 
considerably lower than in a closed vessel as described above. To determine the burning 
point the glass cover is to be removed and the heating continued till the whole surface 
of the oil takes five and must be blown out. The flame should be extinguished quickly 
so that it will .not unduly heat the thermometer and raise the temperature to be observed 
as the burning point. 



312 POWER PLANT TESTING 

(/) Surface in sq. ft. (average) 

Barrel of cylinders 

Cylinder heads 

Clearance and ports 

End of piston , 

Piston rod 

(g) Jacket surfaces or internal surfaces of cylinder heated by 

jackets in sq. ft 

Barrel of cylinder 

Cylinder heads 

Clearance and ports 

(h) Horse power constant for one lb. M.E.P. and one revolution 

per minute 

10. Give description of main features of engine and plant and illustrate 
with drawings of same given on an appended sheet. Describe 
method of governing. State whether the conditions were 
constant throughout the test 



Total Quantities. 

1 1 . Duration of test, hours 

12. Gas or oil consumed, cu. ft. or lbs 

13 . Air supplied in cubic feet 

14. Cooling water supplied to jackets, lbs 

15. Calorific value of gas or oil by calorimeter test, determined by 

. . . .calorimeter, B.T.U 

Hourly Quantities. 

16. Gas or oil consumed per hour, cu. ft. or lbs 

17. Cooling water supplied per hour, lbs 

Pressures and Temperatures. 

18. Pressure at meter (for gas engine) in inches of water 

19. B arometric pressure of atmosphere 

(a) Reading of height of barometer, ins 

(b) Reading of temperature of barometer, deg. F 

(c) Reading of barometer corrected to 32 F., ins 

20. Temperature of cooling water 

(a) Inlet, deg. F 

(b) Outlet " 

21. Temperature of gas at meter (for gas engine), deg. F 

22. Temperature of atmosphere, deg. F 

(a) Dry-bulb thermometer ' 

(b) Wet-bulb thermometer ' 

(c) Degree of humidity, per cent, (see page 331) 

23. Temperature of exhaust gases, deg. F 

How determined 

Data Relating to Heat Measurements. 

24. Heat units consumed per hour (lbs. of oil or cu. ft. of gas per hour 

multiplied by the total heat of combustion), B.T.U 



GAS AND OIL ENGINE AND PRODUCER TESTING 313 

25. Heat rejected in cooling water 

(a) Total per hour, B.T.U 

(6) In per cent of heat of combustion of the gas or oil con- 
sumed 

26. Sensible heat rejected in exhaust gases above temperature of inlet 

air 

(a) Total per hour, B.T.U 

(6) In per cent of heat of combustion of gas or oil consumed 

27. Heat lost through incomplete combustion and radiation per hour. . . . 

(a) Total per hour, B.T.U 

(6) In per cent of heat of combustion of the gas or oil consumed . . . 

Speed, etc. 

28. Revolutions per minute 

29. Average number of explosions per minute How deter- 

mined 

30. Variation of speed between no load and full load 

31. Fluctuation of speed on changing from no load to full load measured 

by the increase in the revolutions due to the change 

Indicator Diagrams. 

32. Pressure in lbs. per sq. in. above atmosphere, 1 cyl 

2 cyl 

(a) Maximum pressure 

(6) Pressure just before ignition 

(c) Pressure at end of expansion 

(d) Exhaust pressure 

(e) Mean effective pressure 

33. Temperatures in degrees F. computed from diagrams 

(a) Maximum temperature (not necessarily at maximum press.) . . 
(6) Just before ignition 

(c) At end of expansion 

(d) During exhaust 

34. Mean effective pressure in lbs. per sq. in. . 

Power. 

3 5. Power as rated by builders 

(a) Indicated horse power 

(b) Brake horse power 

36. Horse power (indicated) actually developed 

First cylinder 

Second cylinder 

Total 

37. Brake horse power, electric horse power or pump horse power 

according to the class of the engine 

38. Friction indicated horse power from diagrams with no load on 

engine and computed for average speed 

39. Percentage of indicated horse power lost in friction 

Standard Efficiency Results. 

40. Heat units consumed by the engine per hour, B.T.U 

(a) Per indicated horse power 

(b) Per brake horse power 



314 POWER PLANT TESTING 



Heat units consumed by the engine per minute, B.T.U. 

(a) Per indicated horse power 

(6) Per brake horse power 

Thermal efficiency, ratio per cent . 

(a) Per indicated horse power 

(b) Per brake horse power 



Miscellaneous Efficiency Results. 
43 . Cubic feet of gas or lbs. of oil consumed per horse power per hour . 

(a) Per indicated horse power 

(6) Per brake horse power 



Heat Balance. 
44. Quantities given per cent' of the total heat of combustion of the 
fuel 

(a) Heat equivalent of indicated horse power 

(b) Heat rejected in cooling water 

(c) Heat rejected in exhaust gases and lost through radiation 

and incomplete combustion 1 

Subdivisions of Item (e) 

(1) Heat rejected in exhaust gases 

(2) Heat lost through incomplete combustion 

(3) Heat lost through radiation and unaccounted 

Data and Results of Standard Heat Test of Gas or oil Engine. 
Short Form 

1 . Made by of 

on engine located at 

to determine 

2 . Date of trial 

3 . Type of engine or class 

4. Kind of fuel used 

(a) Specific gravity 

(6) Flashing point, deg. F 

(c) Burning point 

5 . Dimensions of engines 

(a) Class of cylinder (working or for compressing the charge) 

(b) Single or double acting 

(c) Cylinder dimensions 

Bore ins 

Stroke ft 

Diameter of piston ins 

(d) Average compression space, or clearance in per cent of volume 

displaced in piston per stroke 

(e) Horse power constant for one pound M.E.P. and one revolu- 

tion per minute 

Total Quantities. 

6. Duration of test, hours ■ 

7. Gas or oil consumed, cu. ft. or lbs 

8. Cooling water supplied to the jackets, lbs 

9. Calorific value of fuel by calorimeter test, determined by 

calorimeter, B.T.U 



GAS AND OIL ENGINE AND PRODUCER TESTING 315 

Pressures and Temperatures. 

10. Pressure at meter (for gas engine) in inches of water 

1 1 . Barometric pressure of atmosphere 

(a) Reading of barometer in inches 

(b) Reading corrected to 32 F, ins 

12. Temperature of cooling water, degrees F 

(a) Inlet 

(6) Outlet 

13. Temperature of gas at meter (for gas engine) degrees F 

14. Temperature of atmosphere, degrees F 

(a) Dry- bulb thermometer, degrees F 

(6) Wet-bulb thermometer, " 

(c) Degree of humidity, per cent 

15. Temperature of exhaust gases, deg. F 

Data Relating to Heat Measurements. 

16. Heat units consumed per hour (pounds of oil or cubic feet of gas per 

hour multiplied by the total heat of combustion), B.T.U 

17. Heat rejected in cooling water per hour, B.T.U 

Speed, etc. 

18. Revolutions per minute 

19. Average number of explosions per minute 

Indicator Diagrams. 

20. Pressure in lbs. per sq. in. above atmosphere 

(a) Maximum pressure 

(b) Pressure just before ignition 

(c) Pressure at end of expansion 

(d) Exhaust pressure 

20a. Mean effective pressure, lbs. per sq. in 

Power. 

2 1 . Indicated horse power 

First cylinder 

Second cvlinder 

Total 

22. Brake horse power 

23. Friction horse power by friction diagram 

24. Percentage of indicated horse power lost in friction 

Standard Efficiency and Oilier Results. 

25. Heat units consumed by the engine per hour, B.T.U 

(a) Per indicated horse power 

(b) Per brake horse power • 

26. Pounds of oil or cubic feet of gas consumed per hour 

(a) Per indicated horse power, lbs. or cu. ft 

[b) Per brake horse power, lbs. or cu. ft 

Indicator Diagrams of the Suction Stroke of a Gas or Oil 
Engine. With the ordinary stiff spring used for measuring 



316 



POWER PLANT TESTING 



the horse power of gas and oil engines, very little information 
regarding the action of the valves during the suction stroke 
is obtainable from the indicator diagram. For this reason 
the events in the suction stroke must be obtained with a 
comparatively light spring, which must be protected, however, 
from injury when subjected to the excessive pressure of the 
explosion stroke by inserting a suitable stop of some kind to 




Fig. 213. 



Light Spring " Indicator Diagram of a Gas Engine. 



prevent undue compression of the spring. The device usually 
adopted is to slip a small brass tube over the piston rod of the 
indicator to act as a distance piece. Another method, also 
satisfactory, is to fit a short but very thin brass tube over the 
outside of the spring, but of such a diameter that it will pass 
easily inside the cylinder of the indicator and rest easily on the 
top of the piston. A " light -spring " diagram is shown in Fig. 




Fig. 214. — Normal Indicator Diagram of a Gas Engine. 



213, which was taken from an engine giving an ordinary diagram 
like Fig. 214. In Fig. 213 the lower horizontal line is the atmos- 
pheric line and the upper horizontal line is traced by the pencil 
of the indicator, during the compression and explosion strokes, 
showing the effect of the stop. The wavy line S shows the 
exhaust stroke, and the slightly curved line E is the suction. 
The diagram shows that there was a partial vacuum throughout 
the suction stroke and for a part of the exhaust stroke, the 



GAS AND OIL ENGINE AND PRODUCER TESTING 



317 



the latter effect being due doubtless to the inertia of the gases 
in the exhaust pipe. 

In the 'three figures following very interesting indicator 
diagrams of gas engines due to Pullen are illustrated. Figs. 
215 and 216 show explosions during the suction stroke, gener- 




Fig. 215. — Indicator Diagram of a Gas Engine Showing Explosion in Air 
Pipe. 

ally called explosions in the air pipe, for the reason that since 
the air valve is then open the explosion occurred probably in 
the air pipe. In Fig. 215 the effect of the explosion is shown 
in the indicator diagram by the hump near the atmospheric 
line near the middle of the stroke, while in Fig. 216 the explosion 




Fig. 216. — Abnormal Gas Engine Diagrams. 

occurred near the end of the stroke. Explosions in the air pipe 
are sometimes attributed to there being too weak a mixture 
(too little rich gas) in the cylinder, causing very slow burning 
instead of a sharp explosion. Under these conditions combus- 
tion will not be complete at the end of the working stroke, and 



318 POWER PLANT TESTING 

this slow burning goes on through the exhaust stroke. Then 
when the exhaust valve closes, some of this smouldering gas 
remains in the clearance space, which, when mixed with the 
new charge during the next suction stroke, forms a combustible 
mixture which is easily exploded. In Fig. 216 the explosion 
occurred near the end of the suction stroke at x, and the air valve 
has closed before the pressure has had time to fall to atmos- 
pheric. On this account the compression line c is much higher 
than it would be under normal conditions as shown by b. Since 
no explosion takes place, the curve d corresponding to the 
working stroke lies just below this abnormal compression line. 
No less interesting are the diagrams illustrated in Fig. 217, 
showing the effect of pre-ignition on the indicator diagram of 




Fig. 217. — Indicator Diagrams of a Gas Engine Illustrating the Effect of 
" Timing " (from Preignition to Slow Burning). 

a gas engine. Here in two of the diagrams shown the ignition 
occurred too early or before the end of the compression stroke. 
Under these conditions there is usually a heavy thumping noise 
in the engine cylinder, and the engine will not develop as much 
power as there would be if ignition were " timed " a little later. 
This effect may be caused in poorly designed engines by some 
small metal projection or web in the clearance space becoming 
hot enough to ignite the charge before the ignition device 
operates. On the other hand, the point of ignition may have 
been advanced too far by inexperienced persons. 

Fuels for Gas and Oil Engines. The ordinary type of gas 
engine is generally operated with either illuminating gas or 
natural gas. Since, however, natural gas occurs only in limited 



GAS AND OIL ENGINE AND PRODUCER TESTING 319 

areas its use is very much restricted. Blast-furnace gas is 
used in iron works for operating engines with the waste gases 
from the blast furnaces. Ins gas from coke-ovens, also a 
waste gas, is now being used to some extent in the gas engines 
of power plants in the coke regions. Of the various kinds of 
so-called fuel gases, producer gas is, however, by far the most 
important. Anthracite coal is more easily converted into 
producer gas than any other fuel, although cheap bituminous 
coals are now also used. The apparatus used for generating 
producer gas is called in technical language a producer. There 
are in common use two types of producers for converting solid 
fuel into a permanent fuel gas. In one type the air or the steam 
(or both together) that is required for the operation of the pro- 
ducer is forced under pressure, produced usually by a blower, 
through the bed of solid fuel. In the other type of producer 
the air and water are drawn through the bed of fuel either by 
the suction of the engine itself, or by the suction of an auxiliary 
" exhauster." Gas is made at a more or less uniform rate in a 
pressure producer while it operates and the gas is stored in 
tanks, generally of comparatively small capacity, from which 
it is drawn to meet the varying needs of the engine. A suction 
producer operating without an auxiliary " exhauster " is not 
provided with a storage tank, but the gas is generated at the 
rate demanded by the needs of the engine. 

Producer Gas. The most 'common method for making pro- 
ducer gas to be used in engines is to admit both air and steam 
(or water vapor) simultaneously and continuously to the 
incandescent fuel bed. Another method is to burn the fuel 
for a time with air alone; that is, without any steam, till the 
fuel bed becomes highly incandescent, and then shut off the 
supply of air and pass steam or water vapor into the fuel till its 
temperature becomes so low that very little gas is formed and 
the air must be used again with the steam supply shut off. 
The producer continues in operation by alternating the 
admission of air and steam to the fuel bed. The former of these 
two methods is the one most generally used. 

Suction Gas Producer. Anthracite coal is the most satis- 
factory fuel for suction gas producers, some preferring " chest- 
nut " size, while others get the most satisfactory operation with 
the " pea " size if the coal supplied is clean. A producer or 



320 



POWER PLANT TESTING 



generator for such fuel is illustrated in Fig. 218. It consists 
essentially of a vertical cylinder of cast-iron P lined with fire- 
brick, and having grates near the bottom which are easily 
cleaned and stoked through doors conveniently located near 
the base. A side outlet is sometimes provided for the removal 
of ashes from below the grate ; but in many cases the ashes are 
removed through the stoking doors. It is necessary that the 
producer should be air-tight except for the regular openings 
provided for the admission of air and steam or water vapor. 
In the usual forms of suction producers the " suction " stroke 
of the engine E draws the necessary supply of air and steam or 




Suction Gas Producer and Engine. 



vapor through the incandescent fuel bed, where the chemical 
changes of dissociating the steam and burning the coal occur. 
The fuel gas, as a rule, is conducted in a pipe from the top of 
the producer to the bottom of a " wet scrubber " WS for clean- 
ing the gas by washing it with water. This scrubber is usually 
a vertical cylinder of cast-iron filled with broken coke, or else 
having a large number of wooden slats over which a small stream 
of water trickles from top to bottom. In its passage through 
the " wet " scrubber the soot, dust, tarry and other impurities 
are removed from the gas, after which it passes to a " dry " 
scrubber DS, known also as a " purifier " or "moisture separator," 
in which it passes through a mass of either excelsior, sawdust, 
or fine wood shavings, provided for removing moisture and 



GAS AND OIL ENGINE AND PRODUCER TESTING 321 



such solid particles as were not taken out in the " wet scrubber." 
After leaving the " dry scrubber " the gas should be properly- 
cleaned for satisfactory use in the engine cylinder. A regulator 
or receiver R is needed for providing a volume of gas for expand- 
ing and flowing into the engine E during the suction stroke. By 
this means a comparatively steady flow of gas can be main- 
tained from the producer and the resistance due to pipe friction 
to be overcome during the suction stroke is very much less than 
it would be if no reciever were used. Many producer plants are 



Wet Scrubber 




Fig 219. — Section of Suction Gas Producer with Economizer. 

provided with an economizer located between the producer and 
the wet scrubber, as shown in Fig. 2ig. With this arrangement 
the air before going to the producer passes through this econ- 
omizer, where it receives heat absorbed from the hot producer 
gas. The exhaust from the gas engine is also sometimes used 
for heating the air before it enters the producer. As a result 
of the chemical changes with an insufficient supply of air for 
complete combustion taking place in a producer of the type 
just described, some of the carbon in the coal is not burned 
completely ; that is, to carbonic dioxide, C0 2 , but forms instead 



322 POWER PLANT TESTING 

carbonic oxide, CO. The excess of carbon then combines with 
the oxygen liberated by the decomposition of steam into its 
elements (hydrogen and oxygen). The following reaction 
shows the formation of carbonic oxide from carbon and steam: 

2H 2 + C 2 = 2CO + 2H 2 

2122 volume proportions. 
36 24 56 4 weight " 

This reaction shows further that the volumes of carbonic oxide 
and hydrogen produced by the decomposition of steam are equal 
to each other, and that the total volume of these two gases, 
leaving out of account now the carbonic oxide formed by incom- 
plete combustion, is twice as large as that of the steam used, 
considering, of course, equal temperatures and pressures. 

In the decomposition of steam in the producer more heat 
is absorbed than is produced by the combustion of its carbon 
to carbonic oxide. 1 The extra heat required to make the 
process continuous, is provided by the combustion of part of 
the carbon of the fuel in air as described above. From this 
source the heat carried off in the gas leaving the producer, 
that lost by radiation, etc., is produced. 

In the type of suction producer shown in Fig. 218, the steam 
is generated in a vaporizer which is simply a circular trough of 
cast iron encircling the top of the producer on the inside. This 
arrangement permits a constant gas supply automatically 
regulated to the needs of the engine. When the temperatures 
of the fire and of the gas passing from it are raised more heat 
will be conducted to the vaporizer and the rate of steaming 
will be increased ; but this increased amount of steam delivered 
into the fuel bed will cool the fire to the proper temperature. 
In this way the temperature and composition of the gas can be 
kept fairly constant if the producer is otherwise operating 
properly. In Fig. 219 the vaporizer is in the economizer, but 
here also the rate of steaming is regulated by the temperature 
of the gas leaving the producer, so that the regulation is also 
automatic. 

1 When a pound of carbon is burned to carbonic oxide (CO) only 
4400 B.T.U. are produced, while when the same weight of carbon is 
burned to carbonic dioxide (C0 2 ) the heat developed is 14,650 B.T.U. 



GAS AND OIL ENGINE AND PRODUCER TESTING 323 

In some producers the steam is admitted through pipes 
entering the fuel space some distance above the grate bars. 
This arrangement is used to secure more perfect combustion of 
the fuel than is possible in the usual arrangement, because now 
only air is permitted to come into contact with the fuel in the 
lowest and hottest part of the fuel bed, and a high temperature 
can be maintained without difficulty. In this way it is pos- 
sible to improve the economy of producers which otherwise 
would be operated, so that there would be a considerable 
amount of unburned coal removed with the ashes. 

An air blower or enclosed fan of some kind is required to 
create a draught for starting the fire or for bringing up the 
fire after it has been " idle " for some time. When blowing up 
the fire a vent is opened between the producer and the wet 
scrubber to allow the gas generated to pass off, preferably through 
a chimney. If the plant is provided with an economizer the vent 
should be located so that the economizer will be heated during 
the time required for blowing up the fire. 

Capacity and Efficiency of Gas Producers. The important 
result to be determined from tests of a gas producer is the 
ratio of the heat value of the gas produced (in B. T. U.) 
to the heat value in the same units of the fuel used and the 
mechanical or electrical energy required in producing the gas. 
The capacity or the rate at which gas can be produced is also 
important, since a high rate of gasification means lower initial 
costs of the plant. In reports of tests of gas producers it should 
be clearly stated whether the high or the low heat value of the 
gas has been used in the calculations. There is no accepted 
rule as to whether the high or the low heat value should be used 
in guarantees, so that the one to be used must be clearly stated. 
Probably the best method of stating guarantees is to give the 
amount (volume) of gas at a standard temperature and pressure 
and the heat value (high or low as perferred) per unit volume 
(usually a cubic foot) that a producer and its accessories will 
deliver from a stated weight of coal, of which the heat value per 
pound is also given. Mechanical, electrical, or other energy 
received from outside sources must also be taken into account. 
In the specifications for guarantees it should be stated that the 
loss of unburned fuel in the ash is to be charged as fuel used by 
the producer. 



324 POWER PLANT TESTING 

Commercial and Grate Efficiency. The efficiencies of a 
producer gas plant may be stated in a number of ways, but 
most of the items included will vary with the kind of producer 
used, so that what is known as the commercial efficiency E c is 
the only important one for comparison. Using then the fol- 
lowing symbols, 

h g --meat value of gas made B.T.U. per hour; 
hf =heat value of fuel used B.T.U. per hour; 
h =heat equivalent of energy from outside sources, B.T.U. 

per hour ; 
h b =-heat of fuel actually burned in producer, B.T.U. per 
hour. 

n/ + h 
and the efficiency of the grates ~E g may be stated as 

E„=^ (91) 

The following data of observations and results should be included 
in a report of a test. 

1 . Duration of test, hours 

2. Brake horse power 

3 . Coal fired per hour, lbs 

4. Coal fired per brake horse power per hour, lbs 

5. Coal fired per square foot 1 per hour, lbs 

6. Cooling water per hour, cu.ft 

7. Cooling water per brake horse power per hour, cu.ft 

8. Inlet temperature of cooling water, deg. F 

9. Outlet temperature of cooling water, deg. F 

10. Average temperature rise, deg. F 

11. Heat value of gas by calorimeter, 2 B.T.U 

12. Heat value of gas, maximum, B.T.U 

13. Heat value of gas, minimum, B.T.U 

14. Suction at scrubber, ins. of water 

15. Temperature of gas leaving producer, deg. F 

16. Temperature of gas leaving economizer, deg. F 

17. Mechanical efficiency of engine, per cent 

18. Thermal efficiency of engine, per cent 

19. Efficiency of producer, based on lower heat value of gas, per cent. . . 

20. Heat balance 

1 Rate of gasification per sq. ft. of fuel bed area. 

2 Calorific values are all reduced to standard conditions used for commercial tests at 
62 deg. F. and 30 inches of mercury (barometer). 



CHAPTER XV. 

TESTING OF VENTILATING FANS OR BLOWERS AND AIR 
COMPRESSORS 

Ventilating Fans or Blowers are classified in general into 
one of the three groups designated as follows : 
(i) Centrifugal fans; 

(2) Disk (Propeller) fans; 

(3) Turbine (Sirocco) fans; 

(4) Positive pressure blowers. 

Centrifugal Fans are used almost exclusively when large 
volumes of air are to be handled at a comparatively small 
pressure. Such a fan consists essentially of a number of plates, 





Fig. 222. Fio. 223. 

" Standard " Types of Ventilating Fans. 

either flat or curved, attached to radial arms springing from a 
central hub through which the driving shaft passes, as in the 
" spider " type shown in Fig. 222, or the blades may be attached 
to a conical plate as in Fig. 223. Fans resembling either of 
these two designs are known commercially as the " standard " 
type. The " width " of the blades is, in most cases, parallel 
to the shaft. 

325 



326 



POWER PLANT TESTING 




Fig. 224.- 



-Rateau Ventilating Fan Showing Spiral 
Casing. 



The work performed by a centrifugal type of fan is equal 

to the resistance 
times the veloci- 
ty of flow. Since, 
however, the fan 
resistances are 
proportional to 
the square of the 
velocity, 1 the 
work done is pro- 
portional to the 
cube of the ve- 
locity. Fans of 
this type> are in- 
variably provi- 
ded with an air- 
tight spiral cas- 
ing C as shown 
in Fig. 224, where the suction is at S and the discharge is at 
D. The fan shown 
in this figure repre- 
sents the celebra- 
ted Rateau designs, 
which are exten- 
sively used in Eu- 
rope. 

Disk or Propeller 
Fans are best illus- 
trated by the so- 
called " electric " 
fans so commonly 
used in offices, 
shops and dwell- 
ings. Fans of this 
type are usually of 
a very light con- 
struction with the 
vanes arranged as in a screw propeller for a ship. In many 

1 See Professor Rateau's articles in Revue de M ecanique , vol. 1, pages 
629-837. 




Fig. 225. — Turbine Type (Sirocco) Fan. 



TESTING OF VENTILATING FANS OR BLOWERS 



327 



cases fans of this type are not provided with casings, so that it 
is more difficult to make velocity measurements than with 
centrifugal fans. 

Turbine or " Sirocco " fans have an impeller or fan wheel 
of the " squirrel cage " type, as illustrated in Fig. 225. Fans 
of this type can be designed to give very high efficiencies. 
This is due primarily to two characteristic features adopted in 
these designs. By the use of very short blades a very large 
intake space for the suction is provided which is practically 
unobstructed, thus giving a very free " suction." The other 
important feature of this fan is that the air leaves the blades 




Fig. 226. — Velocity Diagram for a 
Turbine Fan. 



Fig. 227. — Velocity Diagram 
for a " Standard " Fan. 



at a higher velocity than that at which the tips of the blades 
are moving. The importance of this result is shown by a com- 
parison of Figs. 226 and 227. The former illustrates the type 
of blading in a turbine or " Sirocco" fan and shows graphically 
by a velocity diagram, constructed like a parallelogram of 
forces, the velocity of the tips of the blades V&, the velocity 
of radial flow in the blades W and the absolute velocity of the 
discharge V a , which is the velocity of the air with respect to 
the stationary casing. It will be observed that in Fig. 226, 
V a is nearly 50 per cent greater than the velocity of the tips 
Vfc, while in Fig. 227, representing the corresponding velocities 
for a standard type of fan, the absolute velocity of the discharge 
V a is actually considerably less than the speed of the tips of 
the blades. Increased velocity is accomplished in a type of 



328 



POWER PLANT TESTING 



fan like Fig. 226, not only by the curvature of the tips of the 
blades, but also to some extent by making the blades somewhat 
concave with the inner ends (toward the center) practically 
radial. By this method of designing the outer edges of the 
blades have a smaller space between them than the inner 
edges. This has the effect of reducing the area on the discharge 
side of the blades and consequently the velocity of the air is 
increased. 

Positive Pressure Blowers are used principally for blast 
furnaces and smelters where a higher pressure is needed than 
can be efficiently obtained with a centrifugal fan. A section 
showing the rotors and casing of one of the blowers is shown 

in Fig. 228. It is often 
called Root's blower. 
The efficiency of a 
blower of this type de- 
pends on the accuracy 
of the fitting of the 
two rotors, A and B, 
both with respect to 
each other and to the 
casing. It is for this 
reason that when new 
the efficiency is high, 
but after being in ser- 
vice for several years 
the bearings and the 
surfaces of the rotors will become worn, so that there is con- 
siderable leakage and consequent loss of efficiency. 

Tests of Ventilating Fans or Blowers are made usually 
by a very simple method ; that is, by determining the necessary 
data for calculating efficiency by measuring the work done by 
the fan " on the air " in giving velocity, and the power required 
to drive the fan alone, excluding bearing friction. The fan 
is preferably operated by an electric motor, of which the efficiency 
can be readily determined by a Prony brake test. The power 
required to overcome the bearing friction of the shaft of the fan 
may well be first determined by measuring the power input , 

1 For normal operation " friction work " is, for machinery in" general, 
proportional to the speed. 




Fig. 228. — Typical Positive Pressure Blower. 



TESTING OF VENTILATING FANS OR BLOWERS 329 

(kilowatts) for a series of speeds when the keys fastening the 
fan to its shaft have been removed and the fan itself has been 
" blocked " in its casing. The shaft will then revolve in the 
hub of the fan and in the bearings. After attaching the 
fan again to the shaft the input to the motor and the work 
done by the fan " on the air " should be determined for various 
speeds. Then obviously the ratio of the work done by the fan 
divided by the power required to drive it after correction for 
the efficiency i of the motor and bearing friction is the actual 
efficiency of the fan. In general terms this may be stated as 
follows : 

f =input to motor to drive motor and shaft of fan in bear- 
ings, kilowatts; 

i =input to motor to drive motor and fan, in kilowatts; 

e = efficiency of motor for motor input of i kilowatts and at 
speed of test ; 

e' =efficiency of motor for motor input of f kilowatts and 
at speed of test. 
Then if i n is the net work in horse power to drive fan alone, 

ei-e'f . , 

>=^6' • ' • • • • <9 2 > 

If the fan to be tested is direct-connected to a steam engine, 
the test is usually made by measuring the indicated horse 
power of the engine at the various speeds and also with the fan 
disconnected for no load. If it is possible to do so the fan should 
be removed from the shaft for the no-load test to determine 
bearing friction. 

The work done by the fan " on the air," is most readily 
calculated by the same method used to calculate the efficiency 
of hydraulic pumps (see page 357), that is, by multiplying the 
number of pounds of air delivered per unit of time by the head 
in feet of air corresponding to the discharge pressure. This 
product is obviously in terms of work in foot-pounds per unit 
of time, and dividing by 33,000 the corresponding horse power 
is obtained. Using the following symbols, the same results 
may be expressed, however, by the product of " pressure times 
volume " as follows: 

1 Motor efficiency must be necessarily determined for the conditions 
of each test; that is, for the same kilowatts and speed as for each test. 



330 POWER PLANT TESTING 

v = velocity of air in feet per second; 

h =head in feet of air necessary to produce a velocity of v 

feet per second, or, 
=water pressure p in inches observed with a manometer, 

produced by the velocity of the air times the ratio. 

wt. of a cubic foot of water 



wt. of a cubic foot of air 



./— Z — PX62.3 . . 

v=V 2 gh=^2g wtcuftairfort - . . . ( 93 ) 

and V /K = velocity in feet per minute is (taking 2g=64.^) 



Vm ° I096 -W wt.cu.ft P air for test ' ' ' (94) 

Now the velocity in feet per minute V m multiplied by the area 
of the section at which the velocity was observed, gives cubic 
feet C of air discharged per minute, and if P is the total pressure 
(static + velocity) in pounds per square foot then we have for 
j the " air horse power " or the work done by the fan " on the 



CP 



and efficiency of fan E, is 



E^-- ^- ( 9 6) 

In 33,ooo \ n 

Velocity measurements are usually made with a Pitot tube 
consisting essentially as shown in Figs. 136 to 138, pages 143- 
144, of two tubes with openings at the end, arranged so that 
one of them " faces " in the direction of flow and the other 
extends in a radial direction. The former is subjected to the 
sum of the velocity and static pressures, while the latter 
receives only the static pressure. 

1 Weight of air taken for calculation must be that corresponding 
to the total pressure in the discharge pipe, the temperature and the 
humidity. For tables of weight of air see pages 145 and 331, also Kent's 
"Mechanical Engineers' Pocket-Book," 8th edition, pages 583-588, and 
"Calculating and Testing Ventilating Systems," issued by U. S. Navy 
Department, Washington. 



TESTING OF VENTILATING FANS OR BLOWERS 



331 



The following table of relative humidity for determinations 
with a wet- and a dry -bulb thermometer is used by the U. S. 
Weather Bureau: 



TABLE OF RELATIVE HUMIDITY, PER CENT 





Difference between the Dry and Wet Thermometers, Deg. F. 


Dry Ther- 












1 


1 1 






1 1 


















1 




mometer, 
Deg. F. 


1 


2 


3 


4 


5 


6 7 


8 9 10 


11 


12 


13 14 is 


16 


17 


18 


19 


20 


21 


22 23 


24 


26 28 


30 




Relative Humidity, Saturation being 100. (Barometer = 3o ins.) 


32 


89 


79 


69 


S9 


49 


39 


30 


20 


XI 


2 




































40 


92 


■■ 


9S 


08 


60 


52 


4 5 


3 7 


29 


23 


IS 


7 

































So 


93 


»7 


80 


74 


07 


61 


SS 


49 


43 


i« 


32 


27 


21 


16 


n 


5 

























60 


94 


89 


8.1 


78 


73 


68 


<M 


: 


53 


48 


4.3 


3 9 


34 


30 


26 


2 1 


17 


13 


9 


5 


1 














70 


95 


90 


86 


81 


77 


72 


68 


64 


S9 


SS 


51 


48 


44 


40 


36 


33 


29 


25 


22 


19 


1.5 


12 


9 


6 








80 


96 


91 


87 


8, 


79 


75 


72 


(,K 


64 


61 


S7 


54 


So 


47 


44 


4i 


38 


3 5 


32 


29 


26 


23 


20 


18 


12 


7 




90 


96 


92 


89 


85 


81 


78 


74 


71 


68 


65 


61 


S<8 


SS 


52 


49 


47 


44 


41 


.39 


36 


34 


31 


29 


26 


22 


17 


13 


100 


go 


9? 


89 


86 


8.S 


80 


77 


7.1 


70 


68 


65 


62 


59 


56 


S4 


Si 


49 


46 


44 


41 


39 


3 7 


3 5 


33 


28 


24 


21 


no 


97 


93 


90 


87 


84 


81 


T^ 


75 


73 


70 


07 


65 


62 


60 


S7 


55 


S2 


SO 


48 


46 


44 


42 


40 


3 8 


3 4 


30 


26 


120 


97 


94 


91 


88 


8S 


8.! 


80 


77 


74 


72 


69 


67 


65 


62 


60 


5 8 


ss 


S3 


51 


49 


47 


45 


43 


41 


18 


34 


31 


140 


97 


95 


92 


89 


87 


84 


82 


79 


77 


75 


73 


70 


68 


66 


64 


62 


60 


58 


56 


54 


53 


Si 


49 


47 


44 


41 


38 



By using the above table the weight of a cubic foot of air 
for any degree of saturation and temperature can be easily 
calculated from the tables of the weight of dry air and ioo per 
cent saturated air x as given on page 145. 

Anemometers are also frequently used for velocity measure- 
ments of air, but they are not generally so reliable as good Pitot 
tubes. Since, however, the observations can be taken directly 
in feet per minute these instruments are used for nearly all 
work where no great accuracy is expected. 

An example showing the method of calculation for j, the 
work done by the fan " on the air," may assist in making the 
method of calculation clearer. 

A series of Pitot-tube measurements taken at ten different 
places in the cross-section of an air duct shows that the 
"velocity" pressure was .795 and the total pressure 1.09 
inches of water. The observations of barometric pressure 
and temperatures by wet- and dry-bulb thermometers, 
together with the " total " pressure given above, served 
to determine the density or the weight of a cubic foot of 
air at the conditions of the test. Barometric pressure 

1 Somewhat more accurate determinations of the weight of air can be 
calculated by empirical formulas given in Kent's " Mechanical Engineers' 
Pocket-Book," 8th edition, pages 583-588. 



332 POWER PLANT TESTING 

was 29.40 inches of mercury and temperatures of wet- 
and dry-bulb thermometers were respectively 54 and 71 
degrees Fahrenheit. According to the tables of the properties 
of air (see footnote, page 330) this was .07329 pound per cubic 
foot. Velocity of the air V m in feet per minute is therefore, 



V m =1096. 4 A /—^— =3625 feet per minute. 
\ .07329 

The diameter of the pipe was 10 inches, of which the area 
is 0.545 square foot. Cubic feet air discharged per minute (C) 
are 3625X0.545 or 1978. The total pressure P is the "total" 

/i.c 9 \ 
pressure 1 in pounds per square foot or ( ) .491 X 144 or 5 - 66 - 

Work done by the fan " on the air " is, then, 

1978X5-66 
j = — = 0.34 horse power. 

33,000 

Efficiency tests should be made with the fan operating under 
the discharge pressure for which it was designed or for which 
the guarantee was made as the case may be. The efficiency of 
the fan may be considerably higher with a lower discharge pres- 
sure than when connected up in a ventilating system where the 
discharge pressure is comparatively high. 

Testing Ventilating Systems. When tests are to be made 
of ventilating systems precautions should be taken in the exam- 
ination of all ducts and piping to see that they are clear of all 
lumber, rubbish, etc., and that the dampers are properly set. The 
tests consist usually in measuring in each system the ' ' static ' ' and 
the " total " pressures with a Pitot tube with all louvers open. 
These tests should be made with the fan running at high, low 
and three or four intermediate speeds. All the results should 
be checked by plotting a curve with revolutions per minute 
for abscissas and cubic feet of air delivered per minute for ordi- 
nates. This curve should be approximately a straight line 

1 In this expression 13.6 is the specific gravity of mercury, .491 is a 
factor for changing inches of mercury at room temperature to pounds 
per square inch, and 144 is used to change pounds per square inch to 
pounds per square foot. 



TESTING OF VENTILATING FANS OR BLOWERS 333 

passing through the origin if all the louvers have remained open 
throughout the tests. On the same abscissas curves of pressure 
for ordinates will also be of advantage in showing the consistency 
of observations. The location selected for the testing slot to 
be used for inserting the Pitot tube in the mains should be as 
near as possible to the fan; preferably no branches, however 
small, should run off between the fan and the testing slots in the 
mains. Furthermore the testing slots should not be near turns 
and bends and particularly no turns or elbows should be imme- 
diately ahead of a slot, that is, in the direction toward the fan. 
These testings lots should be covered when not in use. 

In the U. S. Navy Department the standard conditions adopted 
for testing ventilating fans and air-supply mains are a pressure 
of 5 pounds per square foot in the moving air at the discharge 
outlet from the fan and a velocity of 2cco feet per minute. 
Air at the standard conditions is to be at 70 degrees Fahrenheit 
and a relative humidity of 70 per cent. Under these standard 
conditions a cubic foot of air weighs .07465 pound. The pres- 
sure of 5 pounds is equivalent to a pressure head of 67 feet of 
standard density air. A velocity of 2000 feet per minute corre- 
sponds to a velocity head of 17.27 feet. Total head against 
which the air is delivered to the supply mains for the standard 
conditions is then 84.27 feet, making a very satisfactory com- 
bination of velocity and pressure head, approaching as it does 
the maximum possible delivery for this pressure head. 

Corrections for Losses of Total Head in Ducts. There is 
always some loss of total head along a duct or pipe due to fric- 
tion. As a result there is a smaller delivery than that given 
for standard conditions. Using the following symbols: 

hf =loss of head in feet due to friction; 
f = coefficient of friction =.ooco 8 in piping of good con- 
struction ; 
1 = length of duct in feet ; 
d = diameter of duct in feet ; 
V TO =velocity of flow through duct in feet per minute. 

h f = j (97) 

' n,25o,oood 



If V w =2000 then ^=.3556-. 
d 



334 POWER PLANT TESTING 

Loss of head in a square duct is usually assumed to be the same 
as for a round one ; but for a duct of rectangular section of which 
the short side is b and the long side is nb, the formula above 
becomes, using 1 and V m as before, 

. 1+n 1 w Vm 2 

h f = XrX (98) 

7 n b 2,250,000 

With the help of these formulas when the size of the main 
ducts and the discharge in cubic feet per minute at each outlet 
are known, the head at each outlet as compared with the 
standard total head of 84.27 feet can be calculated. As a 
" rough and ready " rule it is often stated that for a loss of one 
foot of head there is a loss of six-tenths per cent delivery (cubic 
feet per minute) . 

Testing Air Compressors. The various types of machines 
for compressing air are usually operated either by a steam engine 
or by an electric motor. Power delivered to the compressors 
by the engine or motor is therefore measured by one of the 
methods outlined above for ventilating fans. Work done " on 
the air ' ' may be measured by a Pitot tube or by an anemometer 
in a duct if the discharge pipe is large enough as it leaves the 
compressor. 

Air compressors, particularly of the reciprocating type, 
are designed, as a rule, for operation at considerably higher 
pressures than would be suitable for ventilating fans, and the 
volume delivered must usually be measured in a comparatively 
small pipe. Air at high pressure is generally measured by 
calculating the flow through an orifice, carefully rounded on 
the " entrance " side, by Fliegner's formula: 

w=.530^ (99) 

where w = weight of air discharged per second in pounds ; 
a =least area of the orifice in square inches; 
pi =the initial pressure on the orifice (before expansion in 

the orifice) in pounds per square inch absolute. 
Ti =absolute temperature corresponding to the pressure pi. 
This formula has been found to be very accurate for the condi- 
tions of average practice, but is not to be used when p 2 is less 
than twice the atmospheric pressure. 



TESTING OF VENTILATING FANS OR BLOWERS 



335 



The weight of flow, w pounds per second multiplied by the 
head of air in feet corresponding to the " total " pressure, gives 
the foot-pounds of work " done on the air " per second; and 
this product divided by the net power required to drive the 
compressor is the mechanical efficiency. 

In an air compressor in which the air cylinder is direct 
connected to the steam cylinder the net power required to drive 
the compressor is determined by finding the indicated horse 




Fig. 230. — Crosby High-pressure Indicator (Ordnance Type). 

power of the air cylinder and adding the friction in the air 
cylinder, which in many cases can be assumed to be half the 
difference between the indicated horse power as measured in 
the steam and air cylinders. For use on air compressors operat- 
ing at high pressures special indicators are made. One of the 
best is made by the Crosby Steam Gage and Valve Co., Boston, 
Mass., and is illustrated in Fig. 230. It is similar in design to 
the gas engine indicator illustrated in Fig. 211, page 308, except 
that the piston in the lower cylinder of the indicator is very 



336 POWER PLANT TESTING 

small, only one-fortieth of a square inch in area. This indicator 
can therefore be readily used for pressures as high as 10,000 
pounds per square inch. 

Another method for measuring the volume of the delivery 
of the compressor is to connect the discharge pipe to a large 
air-tight tank, provided, however, with an opening near the 
bottom through which water can be removed. If this tank has 
been filled with water before the test begins and the pressure 
is maintained constant in it by taking out water as air is being 
pumped in, then the cubic feet of water taken out is the same 
as the volume of air put in. This method is also serviceable 
for calibrating nozzles to test the accuracy of Fliegner's formula. 
It will be necessary to use a gage graduated as accurately as 
possible, and if the pressure is not very high a mercury column 
will be most satisfactory, as it will show more quickly small 
variations in pressure. 

Test of an Air Compressor 

1 . Revolutions per minute 

2. Mean effective pressure, steam cylinder, lbs. per sq.in 

3. Mean effective pressure, air cylinder, " " " 

4. Indicated horse power, steam cylinder 

5. Indicated horse power, air cylinder 

6. Mechanical efficiency, per cent 

7. Steam pressure, lbs. per sq.in 

8. Reservoir pressure, 

9. Nozzle pressure, 

10. Temperature of air entering cylinder, deg. F 

1 1 . Temperature of air leaving cylinder, deg. F 

12. Temperature of air at nozzle, deg. F 

13. Temperature of air "outside," deg. F 

14. Temperature of steam calorimeter, deg. F 

15. Temperature of water entering jacket, deg. F 

16. Temperature of water leaving jacket, deg. F 

17. Weight of jacket water, lbs. 

18. Weight of condensed steam, lbs 

19. Heat absorbed by jacket water, B.T.U 

20. Quality of steam 

21. Steam used per I.H.P. per hour, lbs 

22. Theoretical air discharged per piston displacement, cu.ft. per hour 

(at 32 deg. F. and 14.7 lbs. per sq.in.) 

23. Actual air discharged through nozzle, cu.ft. per hour (at 32 deg. F. 

and 14.7 lbs. per sq.in.) 

C1 . , (22) -(23 ) 

24. blip, per cent — r — 

(22) 

25. Volumetric efficiency (23) -f- (22) 

26. Air discharged per I.H.P. per hour, lbs. 



CHAPTER XVI 

TESTING OF REFRIGERATION PLANTS 

Refrigerating machines present a most interesting example 
of the conversion of heat energy. In the simplest forms these 
machines consist of a compressor driven by a steam engine, or 
other motive power, serving to compress a gas or vapor as the 
case may be. This gas or vapor is then passed under pressure 
through a surface condenser, where the cooling water absorbs 
the heat generated in the work of compression and then passes 
into an expanding vessel into which it discharges at a very low 
temperature. Now in order to vaporize any liquid, it is necessary 
to maintain a continual application of heat in order to bring 
about this physical change. To convert a unit weight of liquid 
to a unit weight of vapor at the same pressure the heat required 
is always a constant quantity for the same liquid. Thus, as a 
familiar example, to convert a pound of water at " atmospheric " 
pressure and 212 degrees Fahrenheit into steam at the same 
pressure and temperature requires the application of 970 B.T.U. ; 
and conversely, to condense a pound of steam at this same 
pressure and temperature, it is necessary to abstract 970 B.T.U. 
by contact with a cold body. Steam as the working medium 
in a refrigerating machine would, of course, be impracticable, 
because the lowest temperature resulting from actual conden- 
sation in a workable plant would be very much above the 
freezing point of water ; but there are a number of liquids which 
have a very much lower boiling point than water. Of these 
ammonia (NH 3 ), carbonic dioxide (C0 2 ), and sulphurous dioxide 
(S0 2 ) are successfully used for purposes of refrigeration. The 
use of all these depends on the absorption of their latent heat 
in their conversion from a vapor or gas to the liquid condition. 
In practice, the refrigerating medium most commonly used is 
anhydrous ammonia, although carbonic dioxide is also frequently 

337 



338 



POWER PLANT TESTING 



employed. The latter is preferred usually where ammonia gas 
might be dangerous or otherwise objectionable. 

In the simplest form of refrigerating plant the necessary 
machinery consists of (i) a compressor to raise the gas to the 
necessary pressure; (2) a surface condenser to absorb by means 
of cooling water the heat generated by the mechanical work 
of compression; and (3) an expanding or evaporating vessel 
where the liquid is re-evaporated into a gas and, of course, 
absorbs heat in the operation. A very simple refrigerating 
machine is shown in Fig. 231. It consists of the compressor 
C discharging gas under pressure 1 through the pipe P into the 




Fig. 



-Typical Refrigerating Apparatus. 



condensing coil D, consisting in this simple apparatus of a coil 
of pipe in a tank through which the cooling water circulates. 
An expanding valve V serves for reducing the pressure and 
evaporating the liquid coming from D. The expanding vessel 
or evaporator E consists of a coil of pipe immersed in a tank 
containing the liquid to be cooled. Drops of liquid accumulate 
in the bottom coils of the condenser D, to be discharged through 
the expanding valve V into the evaporator E. Since the com- 
pressor receives its supply of gas from the evaporator, the pres- 
sure in the latter must be less than in the condenser. On this 



1 In order to liquefy any gas or vapor, obviously it is necessary to 
bring the molecules closer together, and this can be accomplished either 
by increasing the pressure or decreasing the temperature or by both. 



TESTING OF REFRIGERATING PLANTS 339 

account, then, the liquid after expanding will begin to boil and 
will absorb heat from the surrounding liquid in its transformation 
into a gas. In such a process the temperature of the cooling 
liquid may become very low. The refrigerating liquid in the 
evaporator will be entirely gasified or vaporized and returns 
finally to the compressor C in this state through the suction 
pipe S, thus completing the cycle of operations. 

After this brief explanation of the principles of the operation 
of a refrigerating machine we can take up a brief discussion of 
the thermal processes as regards the interchangeability of heat 
and work. Using the symbol r for the latent heat of vapor- 
ization of the refrigerating medium in B.T.U. per pound, h for 
the heat imparted by compression in the same units, * w for the 
weight in pounds of the gas or vapor entering the compressor 
in a given time, then, neglecting external losses, wr will repre- 
sent the heat abstracted in the evaporator and h +wr is the 
heat given to the cooling liquid in the condenser. 

In the practical operation of a refrigerating plant the evapora- 
tion is maintained at a very low temperature, and some heat 
must necessarily be given to it by the refrigerating medium 
itself, since it enters the evaporator, in comparison, in a moder- 
ately warm condition. Now if the difference in temperature 
between the condenser and the evaporator is t degrees Fahren- 
heit, a pound of refrigerating medium will give to the evaporator 
st B.T.U., if s is the specific heat of the refrigerating medium; 
and further if w' is the weight of this medium in pounds passing 
into the evaporator in a given time then the heat abstracted 
from the evaporator by the cooling liquid is 

wr — x — w'st, 

where x is the heat in B.T.U. lost by radiation. The term w'st 
is comparatively small in practical machines. If there is no 
leakage then, of course, w' will be the same as w. 

Anhydrous ammonia is most commonly used as the refriger- 
ating medium. It is preferable to many other fluids because 

1 The ratio — is often called the coefficient of efficiency of the refriger- 
h 
ating medium. 



340 POWER PLANT TESTING . 

of its comparatively high latent heat 1 and low pressure of 
vaporization. 

Carbonic dioxide (C0 2 ), commercially known as carbonic acid, 
is a colorless gas without odor when pure, and is furthermore 
quite innocuous and has practically no injurious effect on animal 
tissues. It is injurious only when the proportion of it in air 
becomes so large that there remains an insufficient amount of 
oxygen. On this account, therefore, it is much safer and suit- 
able as a refrigerating medium than ammonia. This gas can 
be readily liquefied either by lowering its temperature or by 
increasing the pressure. At ordinarily low temperatures it 
can only remain in the liquid state when under considerable 
pressure. When the pressure is removed, the heat absorbed 
from surrounding bodies assists in the rapid evaporation of the 
liquid and these bodies become correspondingly colder by this 
loss of heat. 

Carbon dioxide is used only to a limited extent, but it is 
found particularly desirable on shipboard because of the com- 
pactness of the compressor that it requires and its inoffensive 
character when a leak occurs. 

A typical commercial refrigerating plant for making ice and 
operating with a horizontal ammonia compressor is shown in 
Fig. 232. The same descriptive letters used in Fig. 231 serve 
again for marking the important parts. 

The efficiency of a refrigerating machine depends upon 
the difference between the extremes of temperature, but unlike 
heat engines, it has the greatest efficiency when the range of 
temperatures is small and when the final temperature is high. 

When a change of volume of a saturated vapor is made under 
constant pressure in the presence of an excess of the liquid, the 
temperature remains constant. In this case the addition or 
absorption of heat to produce the change of volume causes an 
increase or decrease in the amount of the liquid mixed with the 
vapor. Vapors, even when saturated, if no longer in contact 
with their liquids, having heat added either by compression, by 

1 The latent heat of vaporization of ammonia is 555 B.T.U. at a 
temperature of zero degrees Fahrenheit, while that of carbon dioxide 
is only 123. The corresponding absolute pressures at the same tempera- 
ture are 30 pounds per square inch for ammonia and 310 for carbon 
dioxide. 



TESTING OF REFRIGERATING PLANTS 



341 



mechanical force or from an external source of heat, will behave 
practically like permanent gases and will become superheated. 
On this account refrigerating machines using hquefiable gas will 
give results differing according to the conditions of operation, 
depending primarily upon the state of the gas; that is, whether 
it remains constantly saturated or is superheated during a part 
of the cycle. Some ammonia plants are operated with an excess 
of liquid present during compression so that superheating is 



en Pipe 




w§& 

COMPLETE ICE MAKING PLANT 

Fig. 232. Refrigerating Plant with Ammonia Compressor. 

prevented. This is known in practice as the " wet " or " cold ' : 
system of compression. 



At temp. deg. C . . — ic 
At temp. deg. F . . 14 

Density o . 6492 



Density of Liquid Ammonia. 1 
5 



-5 

2 3 32 41 50 

6429 .6364 .6298 .623c 



15 20 

59 68 

.6160 .6086 



Latent Heat of Evaporation of Ammonia 

h e =555-5 --6137 -o.ooo2i 9 r 2 (in B.T.U. degrees F ) 
Ledoux found h e = 583.33 -.5499^ -0.0001 i 73 T 3 (in B.T.U. degrees F.) 

For experimental values at different temperatures determined 
by Professor Denton, see Transactions American Society Me- 
chanical Engineers, vol. 12, page 356. For calculated values, 
see vol. 10, page 646. 

1 These results may be expressed very nearly by 

= 0.6364 — 0.0014/ degrees Centrigrade. 
0.6502—0.000777/ degrees Fahrenheit.- 



342 



POWER PLANT TESTING 



Specific Heat and Available Latent Heat op Hot Ammonia 

Latent heat at 15.67 lbs. and o degrees F. =550.5 B.T.U. Specific heat 
= 1.096— 0.0012 T (degrees). 



Values at 15.67 lbs. Gage Pressure (Lucke) 



Temperature of 




Correction for 


Available Latent 

Heat for 
Saturated Vapor 
B.T.U. per lb. 


Liquid Supply. Speci 
Deg. F. 


fie Heat. 


Cooling. 
B.T.U. 


5 J 


090 


5-45 


55°-°5 


10 1 


084 


10 


84 


544 


66 


*5 1 


078 


16 


17 


539 


33 


20 1 


072 


21 


44 


534 


06 


2 5 J 


066 


26 


65 


528 


85 


30 1 


060 


3 1 


80 


5 2 3 


70 


35 J 


054 


36 


89 


5i8 


61 


40 1 


048 


41 


92 


5*3 


68 


45 1 


042 


46 


89 


508 


61 


5° ! 


036 


5 1 


80 


5°3 


70 


55 1 


030 


56 


65 


498 


85 


60 1 


024 


61 


44 


494 


06 


65 


018 


66 


17 


489 


33 


70 1 


012 


70 


84 


484 


66 


75 1 


006 


75 


45 


480 


°5 


80 1 


000 


80 


00 


475 


5° 


85 


994 


84 


49 


47i 


01 


go 


988 


88 


92 


466 


58 


95 


982 


93 


29 


462 


21 


100 


976 


97 .60 


457 


90 



The latent heat of saturated ammonia vapor as given by 
Lucke must be corrected in three ways : (1) For the temperature 
of the liquid, which must be cooled from its initial temperature 
to the temperature corresponding to the suction or back-pres- 
sure; (2) for wetness of the vapor, for which the correction is 
5.555 B.T.U. for each per cent of moisture; (3) for superheat 
of vapor in case it leaves the expansion coil (evaporator) at a 
higher temperature than that corresponding to the pressure. 
This correction is additive and is approximately the number of 
degrees of superheat times the specific heat of superheated 
ammonia gas taken as 0.508. 

Leakages of ammonia gas are very objectionable and may 
be dangerous. One of the most convenient and reliable means 
for locating a small leak is to burn a little sulphur at the end 



TESTING OF REFRIGERATING PLANTS 343 

of a stick. Where the sulphur fumes come into contact with 
the ammonia gas a white vapor is observed. 

Efficiency of Refrigerating Machines. The maximum theo- 
retical efficiency E. m of a refrigerating machine is expressed by 
the ratio, 

To 



'Ti-To 



(ioo) 



where Ti is the highest and T is the lowest absolute temperature 
of the refrigerating medium. Another and more practical way 
to express the efficiency of a refrigerating plant is found by 
using as a basis the amount of fuel consumed and the " ice- 
melting" capacity 1 of the plant. If we use the following 
symbols : 

R =refrigeration or "ice-melting" capacity per pound of 
fuel, in pounds; 

w& = pounds of brine circulated per hour, pounds; 

Sb=specifi cheat of brine; 

ti =temperature of brine entering expansion coils, deg. F. ; 

t 2 ^temperature of brine leaving expansion coils, deg. F. ; 

W/ =fuel used per hour, pounds ; 

R= W(V-t 1 ) 

i44w f 

and the capacity C of a machine in tons, of 2000 pounds, of 
refrigeration or ice-melting per 24 hours is 



24 W 6 S(t 2 - ti) 

144X2000 



(102) 



Volumetric Efficiency. The ratio of the actual volume of 
ammonia discharged from the compressor to that calculated 
from the piston displacement is called the volumetric efficiency. 
The following formula deduced from Voorhees 2 gives in most 

1 Ice-melting capacity is a term applied to represent the cold produced 
in an insulated bath of brine, measured by the latent heat of fusion of 
ice, which is 144 B.T.U. per pound. More accurately it is the heat 
required to melt a pound of ice at 32 degrees Fahrenheit'to water at the 
same temperature. The capacity of a machine in pounds or tons of 
" ice-melting " or of " refrigeration " does not mean that the machine 
would make that amount of ice ; but that the cold produced is equivalent 
to the melting of the weight of ice to water. 

2 " Ice and Refrigeration " (1902). 



344 POWER PLANT TESTING ^ 

practical cases the volumetric efficiency E„ of an ammonia 
compressor with a remarkable degree of accuracy : 

--'"fc-W C03) 



1330 

where ti is the theoretical temperature of the gas after com- 
pression, t is the temperature of the gas delivered to the com- 
pressor. Here ti can be calculated from the general equation 
for adiabatic compression where 

t 1 +46o=(t + 46o)f — J.024 .... (104) 

Here pi and p are the absolute pressures of the gas correspond- 
ing respectively to the temperatures ti and t . The actual 
temperature of the gas discharged from the compressor will be 
usually considerably, sometimes 50-60 degrees Fahrenheit, less 
than the theoretical. 

Lucke l has deduced the following formula for the indicated 
horse power (I.H.P.) required per ton of refrigerating capacity, 
expressed in the following symbols : 

p =the mean effective pressure in lbs. per square inch ; 

1 =the length of the stroke in feet ; 

a =the area of the piston in square inches; 

n =the number of compressions per minute ; 
E„=the volumetric efficiency, as defined above; 
w c =the weight of a cubic foot of ammonia vapor at the back 
pressure as it exists in the cylinder when compression begins; 
v c is the latent heat of vaporization available for refrigeration 
(see table page 342); 288,000 =the B.T.U. equivalent to one 
ton of refrigeration ; that is, 2occ X 1 44 ; c ^refrigerating capac- 
ity in tons per twenty-four hours. Then, 

plan 
33,000 
I.H.P. = laIU Wc XVc x6o x ~ ... (105) 

144X288,000 

-S^xf- doe) 

w c v c E, 

1 Proceedings American Society of Refrigerating Engineers (1908). 



TESTING OF REFRIGERATING PLANTS 345 

Ammonia Absorption Refrigerating Machines. Another class 
of refrigerating apparatus, operating by what is known as the 
absorption system, has been installed in some places. It consists 
of a generator containing a concentrated solution of ammonia 
in water. This generator is heated usually by means of a coil 
of pipes taking live steam from a boiler, although frequently 
the exhaust steam from engines is utilized to advantage. In 
this system a weak ammonia vapor passes first into an " ana- 
lyzer " where some of the water is separated from the ammonia 
vapor and then into a " rectifier," where the concentrated vapor 
is cooled, precipitating still more water, and then discharges into 
the condenser coils. The lower coils of the condenser are con- 
nected to the upper part of the " cooler " or brine tank. An 
absorption chamber is provided which is filled with a weak 
solution of ammonia, and this chamber is also connected with 
the cooling-tank. The absorption chamber communicates with 
generator by two tubes, one going to the bottom of the gen- 
erator from the top of the chamber, and the other from the 
bottom of the chamber to the top of the generator. In the 
latter pipe line, a pump is located to force the liquid from the 
absorption chamber, where the pressure is about atmospheric, 
to the generator, where the pressure is from ioo to 200 pounds 
per square inch. In the operation of this apparatus the ammonia 
and water in the generator are first heated by the coil of steam 
pipes, and as the ammonia is freed from the solution the pressure 
rises. When this pressure attains that of saturated vapor at 
the temperature of the condenser it becomes liquefied, con- 
densing also a small amount of steam. A suitable expansion 
valve regulates the flow of the liquefied gas into the refrigerating 
coils in the cooler. As it escapes into these coils it expands 
and is again vaporized, absorbing heat from the liquid or gas 
required to be cooled. Just as rapidly as vaporization goes on 
the gas is absorbed by the weak solution in the absorbing cham- 
ber. The heat in the generator has the effect of separating a 
strong from a weak solution, the greater concentration being 
in the upper part. The weaker portion of the solution is con- 
veyed by the pipe entering the top of the absorption chamber. 
The satisfactory operation of this apparatus depends upon 
careful adjustments and regulation of the flow of gas and liquid, 
controlling in this way the temperature in the cooler, 



346 POWER PLANT TESTING 

Testing of Refrigerating Plants. The primary object of a 
test of a refrigerating apparatus is to compare the refrigerating 
effect with the heat equivalent of the mechanical work and of 
the cooling water or brine. The making of ice is not satisfactory 
for accurate results in a test. The range of temperature should 
not be greater than necessary to secure accuracy in the thermom- 
eter readings. A range of from 5 to 6 degrees Fahrenheit is 
usually sufficient and, in fact, most satisfactory. The brine 
should be measured or weighed in suitable tanks as for the con- 
densed steam in engine tests. 

One of the most important precautions to be observed is 
to determine accurately the specific heat of the brine for the 
temperature range of the test. Small differences in its con- 
centration and composition may produce a considerable varia- 
tion in results. When a compresser and steam engine are coupled 
directly together on the same shaft a direct measurement of the 
power required for the compresser is not obtainable. By measur- 
ing the horse power of the engine running without doing any 
work in the compresser — that is, operating it "empty" — and 
by comparing the differences in power between the steam engine 
and compresser for wide variations of condenser pressure, the 
effective horse power required to drive the refrigerating machine 
can be determined with some degree of accuracy. On account 
of a great deal of external friction being included it is not very 
satisfactory to use for this calculation the horse power of the 
compressor as determined with an engine indicator. 

The following arrangement of data for a test of a refrigera- 
ting plant given by Kent is very useful. It is arranged for tests 
by either the compression or the absorption type of apparatus : 

Report of Test. 

Reports intended to be used for comparison with the figures found 
for other machines will therefore have to embrace at least the following 
observations: 

Refrigerator : 

Quantity of brine circulated per hour 

Brine temperature at inlet to refrigerator, t 

Brine temperature at outlet of refrigerator 

Specific gravity of brine at 64 degrees Fahrenheit 

Specific heat of brine 

Heat abstracted (cold produced) , Q e 

Absolute pressure in the refrigerator ,,.,.. 



TESTING OF REFRIGERATING PLANTS 347 

Condenser: 

Quantity of cooling water per hour 

Temperature at inlet to condenser 

Temperature at outlet to condenser, t c 

Heat abstracted, Q 2 ' 

Absolute pressure in the condenser 

Temperature of gases entering the condenser 

Compression Machine. 
Compressor : 

Indicated work, L c 

Temperature of gases at inlet 

Temperature of gases at discharge 

Steam engine: 

Feed-water per hour 

Temperature of feed-water 

Absolute steam pressure at steam engine 

Indicated work of steam engine, L e . 

Condensing water per hour 

Temperature of condensing water 

Total sum of losses by radiation and convection, ±Q 3 

Heat balance 

Qe+AL^Q^Qg (107) 

Absorption Machine. 
Still: 

Steam consumed per hour 

Absolute pressure of heating steam 

Temperature of condensed steam at outlet 

Heat imparted to still, Q' e 

Absorber : 

Quantity of cooling water per hour 

Temperature at inlet 

Temperature at outlet 

Heat removed, Q 2 

Pump for ammonia liquor 

Indicated work of steam engine 

Steam consumption for pump 

Thermal equivalent for work of pump, ALp 

Total sum of losses by radiation and convection, ±Q S 

Heat balance: 

Qe+Q / e =Qi+Q 2 ±Q 3 (108) 

For the temperatures T and T c at which heat is abstracted 
in the refrigerator and imparted to the condenser, it is correct 
to select the temperature of the brine leaving the refrigerator 
and that of the cooling water leaving the condenser, because 
it is in principle impossible to keep the refrigerator pressure 

1 The term A is the reciprocal of the mechanical equivalent of heat 
(778). 



348 POWER PLANT TESTING 

higher than would correspond to the lowest brine temperature, 
or to reduce the condenser pressure below that corresponding 
to the outlet temperature of the cooling water. 

Professor Linde shows that the maximum theoretical effi- 
ciency of a compression machine may be expressed by the 
formula, 

Q-(AL)=T^(T C -T), (109) 

in which Q = quantity of heat abstracted (cold produced) ; 

AL ^thermal equivalent of the mechanical work ex- 
pended; 
L =the mechanical work; 
A=i^ 77 8; 

T =absblute temperature of heat abstraction (refrig- 
erator) ; 
T c = absolute temperature of heat rejection (condenser). 

If u is the ratio between the heat equivalent of the mechanical 
work AL and the quantity of heat Q' which must be imparted 
to the motor to produce the work L, then 

AL^Q'=u andQ'/Q = (T c -T)-(uT), . . (no) 

It follows that the expenditure of heat Q' necessary for the 
production of the quality of cold Q in a compression-machine 
will be the smaller, the smaller the difference in temperature 
T c -T. 

The following data sheet is used in parts by Denton 1 : 

1. Average high ammonia pressure above atmosphere 

2. Average back ammonia pressure above atmosphere 

3 . Average temperature brine inlet 

4. Average temperature brine outlet 

5 . Average range of temperature 

6. Lbs. of brine circulated per minute 

6a. Specific heat of brine 

7 . Average temperature condensing water at inlet 

8. Average temperature condensing water at outlet 

9. Average range of temperature 

10. Lbs. water circulated per minute through condenser 

11. Lbs. water per minute through jacket 

12. Range of temperature in jackets 

13. Lbs. ammonia circulated per minute 

1 Transactions American Society of Mechanical Engineers. Vol. 12, 
page 356. 



TESTING OF REFRIGERATING PLANTS 349 

14. Probable temperature of liquid ammonia entrance to brine-tank .... 

15. Temperature ammonia corresponding to average back pressure 

16. Average temperature of gas leaving brine tank 

17. Temperature of gas entering compressor 

18. Average temperature of gas leaving compressor 

19. Average temperature of gas entering condenser 

20. Temperature due to condensing pressure 

21. Heat given ammonia: 

By brine per B.T.U. per minute 

By compressor, B.T.U. per minute 

By atmosphere, B. T. U. per minute 

22. Total heat received by ammonia, B.T.U. per minute 

23. Heat taken from ammonia: 

By condenser, B.T-U. per minute 

By jackets, B.T.U. per minute 

By atmosphere, B.T.U. per minute 

24. Total heat rejected by ammonia, B.T.U.- per minute 

25. Difference of heat received and rejected, B.T.U. per minute 

26. Per cent of work of compression removed by jackets 

27. Average revolutions per minute 

28. Mean effective pressure steam cylinder, lbs. per square in 

29. Mean effective pressure ammonia cylinder, lbs. per square in 

30. Average H.P. steam cylinder 

31. Average H.P. ammonia cylinder 

32. Friction in per cent of steam H.P 

33. Total cooling water, gallons per minute, per ton ice-melting capacity 

per 24 hours 

34. Tons ice-melting capacity per 24 hours 

35. Lbs. ice-refrigeration effect per lb. coal at 3 lbs. per H.P. hour 

36. Cost coal per ton of ice-refrigerating effect at $4 per ton 

37. Cost water per ton of ice-refrigerating effect at $1 per 1000 cu. ft.. . . 

38. Total cost of 1 ton ice-refrigeration effect 

39. Refrigeration effect per I. H.P. in compress, cyl., B.T.U. per minute.. 

40. Refrigeration effect per I. H.P. in steam, cyl., B.T.U. per minute. . . . 

41. Refrigeration effect per pound of steam, B.T.U. per minute 



CHAPTER XVII 
TESTING OF HOT-AIR ENGINES 

Hot-air Engines of the conventional type are reciprocating 
' ' piston ' ' engines which are operated by the alternate expansion 
and contraction of a charge of air. This alternate expansion 
and contraction is produced by heating and cooling. Engines 
of this kind now in use are found most often in country places, 
where they are used for pumping water. Usually coal is burned 
for fuel ; but sometimes gas is used, particularly in the natural- 
gas districts. 

Rider Hot-air Engine. The most successful engine of this 
kind is made by the Rider-Ericsson Engine Company of New 
York. This engine, illustrated in Fig. 232, consists of a com- 
pression cylinder C and a power cylinder P, each provided with 
a separate piston. These two cylinders are connected together 
by a rectangular passage R containing a large number of thin 
metallic plates and forming what is called in engines of this type 
the regenerator. This regenerator has for its function the 
alternate abstracting and returning to the air of a quantity of 
heat. Air leaking out is replaced by a fresh supply admitted 
through the check valve V, which opens inward. The com- 
pression cylinder C is provided with a water-jacket. 

The cycle of operations in this engine consist of a compression 
stroke when the piston in the compression cylinder C com- 
presses the cold air from which the heat has been abstracted 
by its passage through the regenerator R,and then by the simulta- 
neous advancing upward movement of the piston in the power 
cylinder P the air passes again through the regenerator and 
also through the heater H without appreciable change of volume. 
As a result the addition of heat increases the pressure of the 
air and when it enters the power cylinder P it pushes the piston 
upward to the end of its stroke. This upward movement of 

350 



TESTING OF HOT-AIR ENGINES 



351 



the power piston in the last half of its stroke carries with it the 
piston in the compression cylinder C, which is on the same shaft 
but set at an angle of 90 degrees, so that the two pistons do not 
reach the ends of their strokes together. Now as the charge 
of air cools the pressure falls, so that the piston in the power 
cylinder falls and in the last half of this stroke carries downward 
with it the piston in 
the compression cylinder 
and again starts com- 
pressing the charge of 
air. As the heated air 
passed through the re- 
generator plates on* its 
way to the compression 
cylinder the greater por- 
tion of the heat it con- 
tained was left in them 
to be abstracted on the 
return movement to be 
used again for increasing 
the temperature of the 
charge. 

In Fig. 232 a water 
pump U is shown at the 
left-hand side of the 
engine. Besides being 
used for supplying a 
water system it pumps 
the cooling water needed 
for the water-jacket T 
and the cooler E. 

Tests of Hot-air En- 
gines do not differ in 
the important details 
from tests of steam and gas engines. The indicated horse 
power is obtained by attaching engine indicators to both 
the power and the working cylinders and the net indicated 
horse power is the difference between that for the power and 
that for the compression cylinders. A Prony brake or similar 
device attached to the main shaft for absorbing the power can 




C— Compression Cylinder 
P -Power Cylinder 
E- Cooler 
H- Heater 
R- Regenerator 
II -Cranks set at about 100° 
J J- Connecting Rods 



L -Check Valve 
M-Pump Primer 
T -Water Jacket, to 

protect packing 

from .heat 
U —Pump 



Fig. 232. Hot Air Engine. 



352 POWER PLANT TESTING 

be used to determine the useful or brake horse power and the 
ratio of the brake to the indicated horse power is the mechanical 
efficiency. 

For testing such engine to determine the efficiencies and 
economy it is preferable to use gas or oil for fuel instead of coal, 
because of the obvious advantages in the determination of fuel 
consumption. 

Therdomynamic efficiency is the ratio of the range of tem- 
perature to the initial absolute temperature of the air in the 
power cylinder. Temperatures not determinable by direct 
measurement may be calculated from the pressures and the 
specific volumes by the general formula for perfect gases, 

T=pv/R, (in) 

where R for air is 53.21. 



CHAPTER XVIII 



TESTS OF HOISTS, BELTS, AND FRICTION WHEELS 



Efficiency of Hoists. An efficiency test of a hoist is made 
by determining the ratio between the work done in lifting the 
load to that applied to the hand chain. Stated briefly, this 
determination is made by raising slowly a known weight, observ- 
ing at the same time by means of a spring balance fastened to 
the hand chain, the pull or force required to keep the load moving 
after it has been started. The method is, of course, the same 
for determining the efficiency of a rope hoist, 
except that some special provision must be 
made for attaching the hook of the spring 
balance to the rope. Allowance must also 
be made, of course, for the number of times 
the power is multiplied, that is, the relative 
velocity value. 

Differential Hoists. Differential hoists 
(Fig. 233), are a little more complicated 
than the ordinary chain or rope hoist. In 
this apparatus, as shown in the standard 
books on the theory of mechanism, the 
velocity ratio is expressed according to the 
dimensions in the figure by, 



2R X 



(112) 




Ri — R 2 

Fig. 233.— Differ- 
It is difficult, however, to measure accurately ential Hoist, 

the radius of these wheels on account of 
the irregular surface made for gripping the links. Now 
since the circumferences of these wheels are proportional to 
the radii, the velocity ratio may be determined by counting 
the number of link-pockets in each of the wheels, and its 
value will be given by the ratio of twice the number of 

353 



354 POWER PLANT TESTING 

link-pockets in the larger wheel divided by the difference 
between the number of link-pockets in the larger and the smaller 
wheels. In some other types of hoists where this method is not 
applicable and the diameters cannot be readily measured, the 
velocity ratio can be determined by tying a piece of string on 
a link of the " load " chain or rope, as the case may be, opposite 
some fixed part of the hoist and mark in the same way a point 
on the chain or rope to which the pull is applied. Now when 
the " load " chain has been moved a measured distance, the 
corresponding movement of the point of application can be 
measured. Several observations should be made to eliminate 
probable errors in the measurements. ' Velocity ratio is usually 
expressed by making the second member of the ratio unity, 
thus 13:1, 4:1, etc. 

The force required to move the hand chain by* the spring 
balance multiplied by the velocity ratio is the work " put into " 
the hoist, while the weight lifted is proportional to the work 
done. Efficiency is then the work done divided by the work 
" put in," or in the terms above is the weight lifted divided 
by the product of the pull on the hand chain times the velocity 
ratio. 1 Determinations should also be made when the load 
is being lowered, but these results should not be averaged with 
those for raising the load because a hoist is generally used only 
for raising loads. 

Determination of Tension in Belts and Rope Drives. Tests 
are often required to determine the power transmitted by 
belts and ropes for specified conditions of load, speed, tension, 
and the coefficient of friction between these and the pulleys on 
which they run. Suitable apparatus for such tests consists of a 
device with which the belts or ropes can be operated with 
different tensions. Power delivered to the follower is generally 
measured with a Prony brake. Usually the load is not increased 
beyond the limit producing 3 per cent slip. 2 The initial 
tension in the belt or rope should be measured when at rest. 
The total tension in motion is the sum of the tensions on the two 

1 If the spring balance is used in the inverted position, its weight 
must be added to the pull. Also the weight of the scale pans used for 
supporting the weights, must be added. 

2 Slip in bolts or ropes is ratio of the difference between the revolu- 
tions of the driver and the follower divided by the revolutions of the 
driver, each taken, of course, for the same time unit. 



TESTS OF HOISTS, BELTS, AND FRICTION WHEELS 355 

sides of the pulley (Ti +T 2 ). Now if Ti and T 2 are equal there 
will be no motion of the belt or rope, but if T x is greater than 
T 2 the motion and the power transmitted will be proportional 
to the difference between (Ti — T 2 ) which is approximately 
expressed by the formula: 

_ 2 (length of brake arm (inches) X net load on brake) 
diameter of driven pulley (inches) 

When Ti +T 2 and Ti — T 2 are both known the separate tensions, 
Ti and T 2 are, of course, readily calculated. 

Tests of Friction Wheels. The apparatus frequently used 
for determining the coefficient of friction between friction wheels 
consists of a pair of pulleys, one of them at least usually made 
of some soft metal like aluminum or a fibrous material like 
straw fiber, leather fiber or paper. This driver runs on a 
follower generally of some other material. Power delivered- to 
the " follower " shaft is absorbed by the Prony brake. A bell- 
crank lever to which weights can be attached is used to hold 
or press the two pulleys together. 

The coefficient of friction as determined by such an apparatus 
is the ratio of the tangential pull to the total normal pressure. 
If the coefficient of friction is represented by f, and other symbols 
are used as follows : 

ri =the effective brake arm in inches ; 

r 2 =the radius of driven pulley ; 

w =net weight on the brake in pounds ; 

p =normal pressure in pounds per inch of width ; 

z = width of the narrower pulley in inches. 

Then, 

wri 

t _KjnL ( > 

pz pr 2 z 



CHAPTER XIX 



HYDRAULIC MACHINERY 



Tests of Hydraulic Machinery 



Tests of Boiler Feed-pumps. In general engineering practice 
there are two classes of pumps commonly used for " feeding " 
the water to steam boilers. These are: 

(1) Motor- or belt-driven pumps ; 

(2) Steam pumps. 

Motor-driven feed-pumps are more generally used in Europe 
than in America, but there are, however, many plants in which 
feed-pumps operated by direct connection to an electric motor 
or by belting from a line shaft are used. Fig. 236 shows a 

good modern example of 
such a pump. It has three 
plungers operated from a 
single shaft with the cranks 
set 1 20 degrees apart. The 
valves are accessible for 
cleaning or for repairs by 
removing the plates or 
" covers " C, C, C. The 
suction pipe is marked S 
and the discharge pipe D. 
An air-chamber A is pro- 
vided to produce, by cush- 
ioning air in it, a somewhat 
more steady flow than 
would be secured without 
it. A relief valve should 
be provided on the dis- 
charge pipe to act as a safety valve in case the pressure in the 
line should get so high that the pump itself might be broken. 

356 




Fig. 236. — Belt-driven Feed Pump. 



HYDRAULIC MACHINERY 357 

The power delivered to a belt-driven pump can usually be 
conveniently measured with a Webber dynamometer or an Emer- 
son power scales (see pages 136—140), while if it is direct-con- 
nected to a motor the efficiency of the motor may be obtained 
by disconnecting it, attaching a Prony brake to the shaft, and 
measuring the input to the motor with suitable electrical 
instruments. 

The equivalent work done " on the water " by the pump is 
found by multiplying the total head * (suction -f discharge) in 
feet by the weight of water lifted (foot-pounds) . 

The quantity of water delivered can be determined by weigh- 
ing or by calculating the flow over a weir or from an orifice (see 
pages 156-161). 

Slip is the difference between the volume swept through by 
the plunger of the pump ; or, in general, the piston displacement, 
and the actual volume of the water pumped at the required head. 

In piston pumps, direct-connected to the steam cylinder 
without a crank, the length of the stroke is usually variable, 
and some special method must be adopted for such tests to 
determine the average length of the stroke. 

Duty of a pump is usually defined as the number of foot- 
pounds of work " delivered " by the pump per 1,000,000 B.T.U. 
supplied. The heat units supplied by the engine are calculated 
by the A.S.M.E. Rules 2 as the product of the weight of feed- 
water used by the boiler and the total heat of steam at boiler 
pressure " reckoned from the temperature of the feed-water." 
The total heat is to be corrected of course for moisture or super- 
heat. 

For a test utilizing a Webber or a similar dynamometer 
belted to the pump for measuring the power the following form 
may be used : 

1 If the discharge head is measured by a pressure-gage on the dis- 
charge pipe then the equivalent pressure in pounds per square inch 
corresponding to the difference in level between the surface of the water- 
supply and the center of the gage must be added to get the total head. 
(One foot head of water at about 62 degrees Fahrenheit is equivalent 
to 0.434 pound per square inch; and conversely, one pound per square 
inch is equivalent to a head of 2.305 feet of water at the above temperature. 
See also foot-note page 361. 

2 More detailed instructions for steam pumps with steam jackets are 
given in Transactions American Society of Mechanical Engineers, vol. 12, 
page 530. 



358 



POWER PLANT TESTING 



Test of a Belt-driven Pump 
(Dynamometer Method) 

i. Type of pump Made by 

2. Diameter of plungers, ins > 

3 . Length of stroke, ft 

4. Size of suction pipe 

5. Size of delivery pipe 

6. Speed of dynamometer, r.p.m. . . . 

7. Speed of pump, r.p.m 

8. Dynamometer reading 

9. Delivery pressure, lbs. per sq.in 

io. Suction pressure, lbs. per sq.in. or inches vacuum. 
1 1 . Temperature of water, deg. F 

Delivery head in feet of water 



13. Suction head in feet of water. 

14. Total head in feet of water 

15. Net weight of water pumped per minute, lbs 

16. Work done by pump, ft. -lbs. per min. (i4)X(is) 



Cubic feet water pumped per minute ■ 

Plunger displacement, cu.ft. per min 

Slip, percent [(18) — (17)]^ (18) 

Net work delivered to pump (by dynamometer) ft. -lbs. per minute, 

Dynamometer horse power, (20) -f- 33 ,000 ■ 

Pump horse power, (16)^33,000 

Mechanical efficiency, (22) -f- (21) ■ 

Capacity of pump, gallons delivered per 24 hours 



A Direct-acting Steam Feed-pump like the one shown in 
section in Fig. 237 will be tested in a somewhat different manner, 
and a different set of observations is required. 




Fig. 



-Direct-acting Steam Pump. 



In none of the so-called direct-acting steam pumps has a 
rotary motion been developed by means of which an eccentric can 
be made to operate the valve. It is, therefore, necessary to 
reverse the piston by an impulse derived from itself at the end of 



HYDRAULIC MACHINERY 359 

each stroke. This cannot be effected in an ordinary single- valve 
engine, as the valve would be moved only to the center of its 
motion, and then the whole machine would stop. To overcome 
this difficulty a small steam piston is provided to move the main 
valve of the engine. 

In these pumps, the lever A, which is carried by the piston 
rod, comes in contact with the tappit when near the end of 
its motion, and, by means of the valve rod R moves the small 
slide valve which operates the supplemental piston. The sup- 
plemental piston, carrying with it the main valve V, is thus 
driven over by steam, and the engine reversed. If, however, 
the supplemental piston fails accidentally to be moved, or to be 
moved with sufficient promptness by steam, the lug on the valve 




Fig. 238. — Outside Packed Plunger Feed-pump. 

rod engages with it and compels its motion by power derived 
from the main engine. 

Outside-packed steam pumps of the plunger type (Fig. 238) 
are now very commonly used for supplying boiler feed-water, 
chiefly because at the pump end the only part subjected to 
ordinary wear is the packing of the plunger stuffing-boxes. 
Steam is admitted at A and exhausts at E. The suction pipe 
is at S and the discharge pipe at D. 

Suitable fittings for the attachment of indicators should' be 
provided at both the steam and the water cylinders. If the 
pump is of the ordinary direct-connected type, without a fly- 
wheel, like the one shown in Fig. 237, some provision must be 
made to make regular observations of the length of the stroke, 



360 



POWER PLANT TESTING 



as it is scarcely ever constant. One method is to attach a 
suitable arm to the cross-head H, Fig. 237, with a pencil at the 
end. Strips of tough paper can then be pasted on a board in 
such a position that the pencil will trace the lengths of the 
strokes. By shifting the position of the board every minute 
or two, records will be obtained from which the average length 
of the stroke can be estimated with considerable accuracy. 
Another method giving still greater accuracy is to use a counting 
device designed by Professor Cooley, operated by a mechanism 
similar to that in a clock (Fig. 240). A cord from the instru- 
ment is attached to the cross-head of the pump and the clock 
mechanism moved by this cord integrates or sums the lengths 




Fig. 240. — Cooley Stroke-measuring Devise. 



of all the strokes. Conditions should be maintained constant 
before beginning a test. 

Form for Steam Pump Test 



Duration of test 

Diameter of steam cylinder. . .. 

Diameter of piston rod 

Diameter of water plunger 

Diameter of plunger piston rod. 



3 
4 

5 

6. Displacement of plunger, cu. ft 

7- 



f Head end . . 
[Crank end. 

Average length of stroke, ft 

Average number of strokes per minute. . . . : 
9. Temperature of water, deg. F 

10. Temperature of feed- water to boiler, deg. F. 

1 1 . Temperature in steam calorimeter, deg. F . . 

12. Feed-water supplied to boiler, lbs. per hour. 

1 3 . Quality of steam 

14. Dry steam supplied to boiler, lbs. per hour. 

15. Boiler pressure, lbs. per sq.in 

16. Delivery pressure, lbs. per sq.in 



HYDRAULIC MACHINERY 361 

17. Suction pressure, lbs. per sq.in. or inches vacuum 

18. Vertical distance between top of suction pipe where suction gage is 

attached and center of gage on delivery pipe, ft. 1 

19. Total head in feet of water. 

20. Weight of water delivered per hour, lbs 

21. Plunger displacement, cu.ft. per hour 

22. Weight of water by plunger displacement, lbs. per hour 

23. Slip of pump, per cent [(21) — (19)]-^ (21) 

24. Coal fired per hour, lbs 

25. Combustible burned per hour, lbs 

26. Steam used per pound of coal, lbs. (actual evaporation) 

27. Equivalent evaporation ("from and at 212 deg. F.") per pound of 

of coal, lbs 

28. Actual evaporation per pound of combustible, lbs 

29. Equivalent evaporation per pound of combustible, lbs 

30. Duty, per 1,000,000 B.T.U 

31. Duty, per 100 lbs. coal fired 

32. Duty, per 1000 lbs. steam (dry) 

33. Capacity, gallons delivered per 24 hours 

34. Mean effective pressure, steam cylinders, lbs. per sq.in 

35. Mean effective pressure, water cylinders, lbs. per sq.in 

36. Indicated horse power, steam cylinders 

37. Indicated horse power, water cylinders 

38. Dry steam used per indicated horse power per hour (steam cylinders) 

Cooley Stroke-measuring Device. An apparatus has been 
developed at the University of Michigan for measuring accu- 
rately the length of the stroke of the type of pumps in which 
steam and water cylinders are direct-connected on the same 
piston rod, such for example as the ordinary steam feed-pumps. 
In such pumps it scarcely ever happens that there are two strokes 
in succession that are of the same length and more or less approx- 
imate methods are usually adopted for obtaining the average 
length of the stroke during a test. With the stroke-measuring 
device referred to above each individual stroke is accurately 
measured and is added by a counting device to the sum of all 
the other strokes that have preceded. As this apparatus is 
used in a test of a variable stroke pump, the reading of the 
counter to the nearest inch can be recorded at the usual 
times for observations. The difference between two readings 
is the total length of all the strokes for the interval between 
observations. If, then, this difference is divided by the total 

1 This is usually stated as the vertical distance between the two gages. A vacuum 
gage, however, on the suction pipe of a pump indicates the vacuum at the level of the 
top of the suction pipe, and not up to the center of the gage. This was shown by Professor 
Cooley by attaching a gage by means of a suitable fitting to the suction pipe of a pump 
so that the gage could be revolved above and below the pipe. It was observed that the 
reading of the gage remained constant, showing that in a suction pipe of a pump the 
water does not rise higher than the top of the pipe. 



362 



POWER PLANT TESTING 



number of strokes for the same time, the average length of the 
stroke can be determined accurately. An assembled view of 
this device is shown in Fig.' 240, and its mechanism is shown in 
Fig. 241, which it will be observed is the same in principle as the 
silent ratchet clutches used for the continuous indicator described 
on page 100. The apparatus is driven by the cord on the wheel 
W, which moves the ratchet wheels B and C in the same way as 




Fig. 241. — Mechanism of Stroke-measuring Device. 

the corresponding parts are moved in the continuous indicator 
referred to. Numbers on the horizontal plate (Fig. 240) are 
feet and those on the circular dial are inches. 

Tests of Centrifugal Pumps. Tests of pumps operating 
against low heads such as single-stage centrifugal pumps are 
suitable for, are made in the same way as explained, for the 
triplex belt-driven feed-pump. It is desired, of course, from the 
results of the tests to compare the power supplied to the pump 
with the work done in lifting the water. Power supplied would 
probably be again measured by some form of transmission 
dynamometer, and the work done is calculated from the weight 
of water delivered and the total head against which the pump 
delivers. 1 

1 For more detailed testing of centrifugal pumps see "Centrifugal 
Pumps," by Lowenstejn and Crissey (D. Van Nostrand Co., 191 1). 



HYDRAULIC MACHINERY 



363 



Centrifugal pumps are frequently driven by direct-connected 
steam turbines.. The horse power required to drive the pump 
is then determined from a speed-power curve of the turbine 
(Fig. 203), page 281, obtained usually from a Prony brake test 
of the turbine. Similarly, if the pump is driven by a variable- 
speed electric motor, a' speed-power curve of the motor can be 
used. Usually, however, when a constant speed motor is used 
it is simpler to determine an efficiency curve of the motor for 
varying power. 

Tests of Impulse Water Wheels. Impulse wheels used to 
operate with water under pressure consist usually of a series of 
buckets attached to the 
periphery of a disk or 
wheel. The btickets are 
usually divided by a cen- 
tral rib so that two "pock- 
ets ' ' are formed (Fig. 242) . 
The curves for each of the 
divisions of the bucket are 
designed to turn the di- 
rection of the impinging 
steam without shock. Fig. 
243 shows a typical im- 
pulse wheel. Impulse 
wheels are designed to 
operate most efficiently 
with high heads. It is, 
therefore, impracticable to 
measure the head directly 
in feet, but it is done 
usually by measuring the 
pressure near the nozzle 

N with a gage. When, the center of the gage is at a 
higher level than the center of the nozzle discharging on the 
wheel, then this difference in level must be added to the head 
calculated from the" gage pressure to determine the total head 
under which the wheel is operating. Power developed is meas- 
ured usually by a Prony brake connected to the shaft S. In all 
tests where a large quantity of water is used, the temperature 
of the water should be recorded and the weight corresponding 




Fig. 



-Bucket of an Impulse Water 
Wheel. 



364 



POWER PLANT TESTING 




Fig. 243. — Typical Impulse Water Wheel. 




Fig. 244. — Water Jet Discharging at High Pressure from the Nozzle of an 
Impulse Wheel. 



HYDRAULIC MACHINERY 365 

should be used. A view of the jet discharged from one of these 
nozzles is given in Fig. 244. The type of impulse wheel most in 
use commercially is called the Pelton, of which typical buckets 
and the engaging jet of water are shown in Fig. 245. 

Laboratory tests for a given head are usually run when 
varying both the load and speed. Make the first test with 
the load on the Prony brake as light as possible consistent 




Fig. 245. — Buckets and Jet of a Pelton Wheel. 

with fairly steady operation of the wheel, and then take a series 
of tests increasing the load in increments to reduce the speed 
about ico revolutions per minute in each succeeding test. 
Duration of tests at each speed should be from twenty to thirty 
minutes with observations taken every two minutes. The 
following from may be used for tests : 

Test of Impulse Wheel 
General Data: 

1. Date 

2. Name of wheel and nominal horse power 

3. Kind of bucket 

4. No. of buckets 

5. Angle of buckets 

6. Diameter of bucket wheel, inches .' 

7. Area of nozzle and delivery pipe 

8. Coefficient of discharge for type of nozzle 

9. Diameter of brake wheel, inches 

10. Length of brake arm, inches 

1 1 . Tare of brake, lbs 

1 2 . Duration of test 

13. Average temperature of water, deg. F 



366 POWER PLANT TESTING 

14. Average pressure by gage at wheel, lbs. per sq.in 

15. Average head at wheel in feet 1 

1 6. Quantity of water for total run in pounds 

1 7 . Quantity of water in pounds per minute 

18. Cubic feet of water per minute 

19. Foot-pounds of work per minute calculated from (15) and (17) 

20. R.P.M : 

2 1 . Net weight on brake, lbs 

2 2 . Horse power as measured by brake 

23. Over-all efficiency of motor, per cent (22) -=- (19) X33, 000 

1 Corrected for vertical distance from the center of the gage to the center of thenozzle. 

Curves. Plot a curve for each head with speed for abscissas 
and ''efficiency per cent for ordinates, also curves for the ratio 
of the velocity of the periphery of the wheel v p to the theoretical 
velocity due to the head v. t ; that is, v p /v t for abscissas and the 
maximum horse power developed for ordinates. 1 

Tests of Water Turbines. A typical reaction turbine is 
shown in Fig. 246. The power is transmitted by the main 
shaft and the smaller shaft is used for controlling the gates 
regulating the quantity of water passing through the wheel. 
For testing, a Prony brake can be placed directly on the vertical 
shaft. In some respects a rope brake is most suitable, as one 
end can be attached to a spring balance and the other end can 
be led over a pulley, and will thus support weights on a vertical 
hanger. It is preferable to have the lower web of the brake- 
wheel solid, that is, without arms, so that it will retain the 
cooling water, which should be arranged to flow into it at 
the rate required. 

Power supplied is determined by the weight of water used 
and by the head under which the wheel operates. These 
quantities are determined in the same general way as for a test 
of an impulse wheel, already described, except in the case of 
a reaction turbine, where the housing or casing in which the 
wheel is placed is always completely filled with water (Fig. 247). 
' With this arrangement the turbine receives not only the effect 
due to the pressure-head, measured from the level in the head- 
race to the center of the wheel, but also that due to the suction 
head, measured from the center of the wheel to the level in the 
tailrace. Data can be recorded in a form similar to that for 

1 Plot curves showing effect of head on efficiency if several tests are 
- run at different heads. 



Hydraulic machinery 



367 



tests on impulse wheels. A typical runner for a reaction turbine 
is shown in Fig. 248. 

Curves. Plot a curve for each gate opening at a constant 
head with speed for abscissas and efficiency per cent for ordinates. 

Tests of Hydraulic Rams. A section of a typical hydraulic 
ram is shown in Fig. 249. It consists of an air chamber H, 




Fig. 246. — Typical Reaction Water Turbine. 

to which is connected the discharge pipe I. There is a check 
valve G opening into the air chamber from the lower chamber 
A into which water is brought by the pipe S. There is a waste 
valve at B. This valve is weighted and opens inward. By 
means of a nut J on the stem of this valve the lift or amount of 
opening of the valve can be regulated. When water is supplied 



368 POWER PLANT TESTING 

to the ram, it escapes through the waste valve B with a velocity 
corresponding approximately to that due to the head under which 
the water is supplied. The effect of this velocity head is to 
reduce the pressure on the upper side of the valve so that it 
becomes unbalanced and closes suddenly. Then the momentum 
of the column of water in the pipe S becomes sufficient to open 







Fig. 247. — Reaction Turbine with Submerged Housing. 

the valve G, and will discharge some water into the discharge 
pipe I against a considerable head. As soon as the pressures 
become equalized the valve G closes, the waste valve B opens 
and water from the supply pipe is again " wasted." This 
alternate action is produced with regularity, and as a result 
the water in the supply pipe acquires a certain " backward and 
forward " wave-motion. As the rule is generally stated the 
length of the supply pipe leading from the reservoir to the ram 



HYDRAULIC MACHINERY 



369 



must be at least five times the head. This length is necessary 
to secure some resistance to this " backward and forward " 
wave-motion. A small air chamber shown at P, with a check- 
valve C opening inward to supply air, is provided in many 
of these rams, as it improves the efficiency. The rate of opening 
of the waste valve or the number of pulsations in a given time 
can be varied by changing the weight on its stem. This appara- 




FiG. 248. — Typical Runner of a Reaction Turbine, 
tus is tested usually by measuring the supply and the discharge 
heads, the weight of water discharged through the delivery 
pipe Wi and that passing through the waste valve w 2 in pounds 
per minute. Then the available energy in the water is 
(Wi +W2)h s , where h s is the supply head; and the useful work 
is Wihd, where h d is the discharge head, 1 then, 

Wih d 



Efficiency 



(wi +w 2 )h s 



(ii5) 



1 Both the supply and the discharge heads must be measured, of 
course, from the same datum or " zero " level. 



370 



POWER PLANT TESTING 



and the capacity Q in gallons per twenty-four hours is Q = 
1440 Wiq, where q is the fraction of a gallon of water in a pound. 
Satisfactory runs of twenty minutes' duration can usually be 
made, each run being made with a different lift or " stroke " 
of the waste valve B. Observations of the heads should be 
taken every five minutes if they are variable, and weighing 
as often as necessary, depending on the size of the tanks used. 
The effect on the efficiency of increasing the lift or " stroke " 
of the waste valve from one-eighth inch by increments of one- 
eighth inch is very interesting. 




Fig. 249. — Section of a Simple Hydraulic Ram. 

Curves. Plot curves with length of " stroke " as abscissas 
and take for ordinates: 

(1) Efficiency; 

(2) Capacity in gallons per twenty-four hours; 

(3) Strokes per minute. 

Fig. 250 shows a slightly different form of ram, as made 
commercially. The principle of operation is, however, the 
same as the one in Fig. 249. Letters used for marking the 
parts are the same in the two figures. 

Tests of Pulsometers. A type of steam pump called a 
pulsometer is illustrated in section in Fig. 251. In the form 
shown here it consists of two chambers AA, joined by tapering 
necks into which a ball C is fitted so as to move in the direction 
of the least pressure between seats in these tapering passages. 



HYDRAULIC MACHINERY 



371 



The chambers AA, on opposite sides, are connected by means of 
check or clack valves EE with the " induction " chamber D. 
Water is delivered through the passage H, which is connected 
to the chambers through the valves G. Between the chambers 
is also a vacuum chamber J, connecting them with the ' ' induc- 
tion " chamber D. Small air valves, moving inward, supply 
air to the chambers AA by opening when the pressure is less 





Fig. 250. — Commercial Type 
of Hydraulic Ram. 



Fig. 251. — Steam Pulsometer. 



than atmospheric. Its operation is explained briefly as follows: 
Starting with the left-hand chamber full of water and with a 
vacuum in the right-hand chamber, this latter chamber will fill 
with water which by its momentum due to rushing in suddenly , 
pushes back the valve C toward the left. Now during this time 
steam has entered the left-hand chamber to the left of the valve 
C (before it has shifted) and by exerting a pressure on the 
surface of the water it forces it through the check valve G, first 
into the delivery passage H and then into the air chamber J. 
Then the steam in this left-hand chamber condenses in contact 
with the cold water and forms a vacuum, permitting the repeti- 



372 POWER PLANT TESTING 

tion of this cycle of events, except that the operations in the two 
chambers are reversed. 

Since all the steam used is condensed and discharged with 
the water lifted, the analysis of the operations in a pulsometer 
are similar to those in the familiar types of injectors, except 
that the steam acts in the pulsometer by pressure instead of by 
impact as in the injector. 

Using the following symbols : 

w s = weight of dry steam, pounds; 
w w = weight of water lifted, pounds; 

ti =temperature of the water supply, deg. Fahr. ; 

t 2 =temperature of the water delivered, deg. Fahr. ; 

r =the latent head of evaporation of the steam in B.T.U.; 

t s =the temperature of the steam, deg. Fahr. ; 

hi =the suction head, feet ; 

h 2 =the delivery head, feet ; 

hi +h 2 =the total head, feet, then 

w s (t s -t 2 +r)=w w (t 2 -ti) (i 16) 

The heat equivalent of the mechanical work done is in B.T.U., 

— -(w^hx + (w s +w w )h 2 ), 
778 

and the heat expended is in B.T.U., 

w s (t s -t 2 +r), 

and 

™. 1 1^.0= • w t „hi + (w s +w w )h 2 . . 

Thermal Efficiency = —±, — ' ^ \. . . (117) 

y 778(w s (t s -t 2 +r)) v " 

And if we neglect the work done in lifting the condensed steam, 
Efficiency -^^ .... ("8) 

Curves. Plot with discharge pressures for abscissas curves 
with both thermal efficiency and capacity (gallons per twenty- 
four hours) as ordinates. 

Tests of Injectors. The injector is known particularly in 
stationary service as the device used for pumping water into the 
boiler when the feed-pump fails. One of the various forms of 
injectors sold commercially is shown in Fig. 252. The steam 



HYDRAULIC MACHINERY 



373 



supply, the suction or water supply, the delivery or discharge, 
and the overflow are marked clearly. A double-tube injector, 
shown similarly in section in Fig. 253, has the parts marked 
in the same way as in the preceding figure. 

Method of Operating Injectors. The method to be given, 
although applicable particularly to the ones described, is, how- 
ever, more or less generally applicable to all makes. Open wide 

both the steam- and 

water-supply (suc- 
tion) valves. Then 
close the water-supply 
(suction) valve slowly 
till the overflow ceases 
(for the type shown 
by Fig. 252) ; or (for 
the type of Fig. 253) 
pull the starting lever 
back a short distance 
until water appears 
at the overflow and 
then continue the 
movement steadily as 
far as the lever will 
go . Regulate the rate 
of delivery by closing 
the water-supply (suc- 
tion) valve. Before 
testing an injector 
or indeed even before 
trying to operate a 
and particularly the 




Fig. 252. — Single Tube Steam Injector. 



new injector, inspect the pipe fittings 
valves on the water-supply pipe to 
observe whether they are tight. It is not at all unusual 
to find that the valve is not air tight, and for this reason it is 
a very good practice to put always some new wicking in the 
space for packing around the stem of the valve on the water- 
supply pipe ; and turn up the cap over the packing tightly. 

Method of Testing. For the testing of injectors, the arrange- 
ment of apparatus consists usually of two barrels supported on 
platform scales, or carefully calibrated tanks fitted with gage 
glasses. During a test the injector draws water from one barrel 



374 POWER PLANT TESTING 

or tank and discharges it into the other. A test of an injector 
must be made, of course, with established conditions; that is, 
with a flying start. This may be accomplished by having the 
injector draw water from the supply tank, but discharge water 
through a by-pass connection on the discharge pipe till the test 
is to begin. For this preliminary operation of the injector the 
level in the supply tank can be maintained very closely, at any 
point marked by manipulating a " quick-opening " valve. 
When the test is to begin, close as quickly as possible this valve 
on the pipe discharging into the supply tank and turn the dis- 
charge from the by-pass into the delivery tank. To make this 
adjustment all the valves to be operated should be of the ' ' quick- 
opening " type. The pressure against which the injector is to 
operate is secured by throttling the discharge pipe by means of 
a globe or an angle valve placed between the injector and the 
by-pass on the discharge pipe. The quick-opening valve would 
not be satisfactory. The suction head is measured from the 
middle of the injector to the average level of the water in the 
supply tank. The discharge head is obtained by adding to 
the head in feet corresponding to the pressure indicated by the 
gage the distance in feet from the center of the gage to a horizon- 
tal line through the middle of the injector. The temperatures 
of the water in the supply and delivery pipes must be observed. 
The injector is stopped at the end of the test by closing the 
steam valve. 

The following form, similar to the one used at Purdue Uni- 
versity, is very complete. Notes explaining the calculations 
required are given above : 

Test of an Injector 

Make of injector Date 

Number 

Size of connections: steam in. dia. ; water in. dia. ; 

discharge in. dia. ; area of discharge ( =a) sq.in. 

Diameter (minimum) of lifting tube in.; forcing tube in. 

a. Duration of test 

b. Steam pressure (average) pounds gage, p s 

c. Delivery pressure (average) pounds gage, p 2 

d. Maximum pressure against which injector will discharge, /> ma x 

e. Suction-head (average) , feet, li l 

/. Delivery-head (average) , feet, /z$ 

g. Temperature of supply (average) t l 

h. Temperature of delivery (average) t 2 

i. Pounds water supplied per hour, w w < 



HYDRAULIC MACHINERY 375 

/. Pounds water and. steam delivered per hour, w m 

k. Cubic feet of water delivered per hour, Q „ 

/. Wet steam per hour, w s ( =w m —w w ) ■ 

■hi. Dry steam per hour, w' s ( =xw s ) , 

n. Water delivered per pound wet steam, pounds ( =w w -i-w s ) 

o. Water delivered per pound dry steam, pounds ( = ic w -t-w' s ) 

p. Velocity of discharge, feet per second, v{ = 144(3-^36000) 

q. Energy delivered, raising injection water, B.T.U. per hour 

r. Energy delivered, heating injection water, B.T.U. per hour 

s. Energy delivered, velocity of discharge, B.T.U. per hour 

t. Total energy delivered, B.T.U. per hour 

u. Energy supplied, B.T.U. per hour 

v. Thermal efficiency as a boiler-feed apparatus 

w. Thermal efficiency as a pump 

x. Horse power 

y. Dry steam per horse power per hour, pounds 

The energy of raising injection water = [w w (h 1 + h 2 ) + w s h 2 ]-r- 778, B.T.U. 
per hour. 

The energy of heating injection water =w w (q 2 — q 1 ) where q x and q 2 corre- 
spond to t A and t 2 ., B.T.U. per hour. 

The energy of discharge =w m v 2 -i- (2gX778), B.T.U. per hour. 

The total energy delivered = item q + item r + item 5. 

The energy supplied = w s (xr s +q s — q 2 ) l where r s and q s correspond to 

p s , and q 2 corresponds to t 2 . x = quality of steam. 

The thermal efficiency as a boiler feed apparatus = 100 X . 

item v 

. item q + item s 
1 he thermal efficiency as a pump = 100 X . 

item v 

rp, , w w (h l + h 2 )+w s h 2 

I he horse power = (120) 

60X33,000 
The dry steam per horse power, per hour =w s ' -f-item x. 

1,000,000 + item p 

I he pump duty = 

item t 
r,ooo,ooo[a' K: .(iii + /i 2 ) +w 8 h 2 ] 
778w s (xr s +q s -q 2 ) 
The weight of steam found by direct weighing may be checked, 
by calculating (assuming radiation loss negligible) a " heat 
balance " in which this weight will be the only unknown, thus 
for this condition, 



(121) 



w s (xr s + q s - q 2 ) = -i- w w {h Y + h 2 ) + w s h 2 + (w w + w s ) V — 
77 8 L 2 S] 

w w \h 1 + h+ 7 l8(q 2 ~q 1 ) + 7 ^] 



+Ww(q2-qi), 

or, approximately, 



71&(xr v + q.-q 2 )-h2 ' ( " 9) 



CHAPTER XX 
TESTING THE STRENGTH OF MATERIALS 

Machines for Testing the Strength of Materials consist, in 
general, of (i) a power system for producing in the specimen 
tested the required stresses, and (2) a weighing system to deter- 
mine the amount of power applied. In the usual form of testing 
machine the load is applied to the specimen through a train of 
gears and screws operated either by power or by hand, depend- 
ing, of course, largely on the capacity. The stress is measured 
by balancing the force exerted on the specimen by a poise 
adjusted at the end of a system of levers just as weight is deter- 
mined with a platform scales. The general principle of most 
machines for testing materials is illustrated in a simple form in 
the apparatus for calibrating indicator springs, Fig. 99, page 
107. In this case the power is applied to the hand wheel, 
which exerts two forces equal but opposite in direction, one 
compressing the spring in the indicator and the other pressing 
on the platform of the scales. 

A diagrammatic view of a typical machine for testing 
materials in tension and compression is shown in Fig. 255. It 
consists essentially of a table T, to which the upper " head " 
A is rigidly attached by means of the vertical bars DD. Heavy 
vertical screws SS, carrying the lower cross-head B are moved 
up or down by the system of gears GG. Moving the cross-head 
B downward puts a tensile stress on a test specimen s if it is 
attached firmly to both the upper " head " A and to the cross- 
head B. The force applied to the specimen is transmitted by 
the bars DD to the weighing table T, which rests on the first 
weighing lever M, having a fulcrum at F. The load on the 
table T is applied to the lever M at the middle of the table. 
The long arm of this lever is connected by means of a short link 
to a second lever N, and this again is connected to the short arm 
of the lever Q at the other end of which the weighing poise P is 

376 



TESTING THE STRENGTH OF MATERIALS 



377 



to be balanced. The position of the poise on this last lever 
(scale beam) indicates the force applied to the specimen s. 

Fig. 256 is a remarkably good illustration for showing the 
parts of a standard testing machine and for explaining its 
operation. Vertical screws SS, connected by gearing to the 
power system, move the cross-head B up or down according to 
the direction of motion. The speed of these screws is controlled 
and their motion reversed by manipulation of the levers marked 




Fig. 255. — Diagram of a Simple Machine for Testing the Strength of 
Materials. 



li, 1 2 , and 1 3 . The vertical columns supporting the upper 
" head " A are bolted to the table T, which rests on the system 
of levers M, N, 0, and Q. The poise P is moved on the lever 
or scale-beam Q by means of a cord connected to the hand wheel 
W. The levers are balanced ' ' to zero ' ' by means of the counter- 
poise C. Adjustment for use with long or short specimens is 
secured by raising or lowering the upper head A. To prevent 
sudden jarring of the machine when the load is released by the 
breaking of a specimen, vertical rods fastened to the base pass 
up loosely through holes in the table T ? at its four corners, and 



37S 



POWER PLANT TESTING , 



on their ends large " check-nuts " are screwed. When the 
machine is in use these nuts must be loose, otherwise they will 
cause a pressure on the table causing the indication ol the scale- 
beam to be greater than the weight due to the load on the speci- 
men. 

Small testing machines with a capacity not exceeding 50,000 
pounds are made to operate by hydraulic pressure. In this 




Fig. 256. — Standard Testing Machine. 



type of machine the movable head applying the load to the 
specimen is moved by the pressure on a piston in a hydraulic 
cylinder. This hydraulic pressure is produced usually in a 
small hand-operated pump at the side of the machine. Oil 
is generally used for the working medium. In order to return 
the oil to the pump from the cylinder, when the pressure is to 
be released, a small check valve controlled by a lever or a screw 
is usually provided. Machines operating hydraulically are not 



TESTING THE STRENGTH OF MATERIALS 



379 



satisfactory for large loads, because the leakage from the cylinder 
is likely to be excessive. 

When a specimen is to be tested in tension its upper end is 
fastened into the wedges or " jaws " in the upper " head " and 
its lower end is similarly gripped in the lower or movable cross- 
head. For tests in compression the specimen is placed between 
the movable cross-head and the table. Transverse loads can 
be applied to long wooden or metal beams with the machine 
shown in Fig. 256, by placing the beam between the supports 
or abutments UU', and applying 
the load by means of the 
movable cross-head B. Usually 
a special fitting with a blunt 
but " definable " edge to local- 
ize the load is inserted into the 
cross-head B for such tests. 

Extensometers. Some of the 
physical properties of materials 
are determined by the rate of 
deformation of the specimen as 
the stress is applied. To meas- 
ure the deformation some very 
accurate instruments have been 
devised, one of which is shown 
in Fig. 257. It consists essen- 
tially of a pair of clamps CC, 
fitted with sharp-pointed thumb- 
screws for attaching them to 
the specimen SS. Two rods B 
and B', fitted to the upper clamp 

on opposite sides of the specimen, are provided at their lower 
ends with adjustable points to be screwed up or down by means 
of the small milled wheels W and W. Opposite these rods 
and fastened to the lower clamp are two micrometer screws, 
usually graduated to ten-thousandths of an inch, for measuring 
the elongation of the specimen. Electrical connections are 
made, as shown, with a battery and a bell. As the 
specimen stretches out the contact points at P and P' are 
moved apart and the distance the micrometer screws are 
raised measures the elongation. With the help of the bell 




Fig. 257. — Extensometer. 



380 



POWER PLANT TESTING 



it is possible to make, for all observations, uniformly light 
contacts. 

Deflectometer. A very simple device for measuring the 
deflection of beams is shown in Fig. 258, consisting of a plate 
P supported upon a steel bar attached to the end supports 
UU\ Deflections can be measured with this apparatus with 



s 



a 



Fig. 258. — Simple Device for Measuring the Deflection of Beams. 

the aid of ordinary "inside " calipers, micrometer calipers, or 
with a special deflectometer. This instrument, illustrated in 
Fig. 259, is often used to measure the deflection of wooden and 
metal beams subjected to transverse stress. It can also be 
used with success to measure the contraction of short specimens 
in compression. 




Fig. 259. — Deflectometer. 



Physical Properties of Materials Defined. The elastic limit 

is a more or less definite value of the unit stress beyond which, 
as the stress is increased, the increase in deformation is greater 
relatively than the increase in stress ; and further, at this point, 
the deformations produced will not disappear entirely when the 
stress is removed. Permanent set or " set " is used to represent 
the lasting deformations produced by stresses greater than the 
elastic limit. 



TESTING THE STRENGTH OF MATERIALS 381 

Modulus of Elasticity is a term used to express the ratio 
of the unit stress to the deformation per unit of length 1 accom- 
panying that stress, within the elastic limit. For example, 
if f is the stress in pounds per square inch within the elastic 
limit and s is the accompanying deformation per inch of length 
in inches, then the modulus of elasticity, in pounds per square 
inch, is 

E=f/s (122) 

The total stress under which a body fails is called its ultimate 
strength ; and the corresponding unit stress is called the ultimate 
unit strength, or, for short, simply the ultimate strength. The 
ratio of the total elongation of a body to its original length is 
called the percentage of elongation. It is obviously the same 
as the term unit deformation. For calculations of percentage 
of elongation, measurements are taken, according to convention, 
between two gage marks usually 8 inches apart. This percentage 
of elongation is a measure of the ductility of the material tested. 
The ratio of the smallest area after rupture to the original area 
is called the " reduction of cross-section." 

Resilience, often called the modulus of resilience, is a term 
used to represent the potential energy stored in a body ; or, from 
another viewpoint, it is the amount of work that can be done by 
the body when relieved from a state of stress. More specifically 
however, it is taken to mean in practice the work, in foot- 
pounds, done on a cubic inch of a material in stressing it to the 
elastic limit. For any value of the load, the resilience is equal 
to the product of half the stress in pounds per square inch at the 
elastic limit times the distortion (usually the elongation) of 
the test-piece in feet per inch of length up to the elastic limit, 
the latter term being the space passed through. Values of 
resilience calculated as thus defined may be checked by com- 
paring with the square of the unit stress at the elastic limit 
divided by 2 4 times the value of the modulus of elasticity (E) . 

Forms of Test-pieces for Tension Tests. Specimens for 
testing should be prepared with a great deal of care. Standard 
forms for round and flat bars 2 for tension tests are shown in Figs. 

1 This unit deformation is often called the unit elongation for slender 
test-pieces, and more generally the strain. 

2 See "Materials of Construction," J. B. Johnson. 



382 



POWER PLANT TESTING 



260 and 261. On such test-pieces marks one inch apart are 
usually made between the limits of the so-called gage length 
AB, which is generally 8 inches. A standard scale similar to 
the one in Fig. 262 is of great assistance in marking a test-piece. 
At the left-hand end a percentage scale is shown from which the 



-Not lass than 




Fig. 260. — Standard Round Bar for Tension Tests. 

percentage of elongation, in a length of 8 inches, can be read 
directly. 

The relation between the gage length AB, and the diameter 
is for round sections, l=8d, and for square sections 1 =gbt. 
Machine work on specimens for testing should be done carefully, 




Piece to he same thickness as plata 
Fig. 261. — Standard Flat Bar for Tension Tests. , 

so that the material is not torn or weakened in other ways. If 
there is any flaw, marked irregularity or other defect in the 
material, the test-piece should be rejected. After, however, 
a test-piece has been '•' necked " and broken as shown in Fig. 

263, the elongation cannot be 
measured very accurately with 
such a scale . One method is to 
measure the elongation from 
the point of rupture toward 
each end. In materials in 
which the ' ' necking ' ' effect is very marked the measured amount 
of elongation will vary according to the distance of the fracture 



n ^!r \WiVr\ 4 r\ Wrx pj 



Fig. 



262. — Scale for Marking Test- 
pieces. 






TESTING THE STRENGTH OF MATERIALS 383 

from the gage marks A and B. If the fracture is midway 
between these marks then nearly all the elongation will be 
between these marks ; but if the fracture is near one of the gage 
marks then a great deal of the elongation will fall outside of 
the marks, so that the measured elongation is too small. To 
correct for these discrepancies mentioned, a so-called " equiv- 
alent elongation " is calculated by the following method: 

Assume that the standard test-piece, Fig. 260, has been 
divided originally into 8 equal spaces between the gage marks 
A and B, and that the nearest number of spaces between the 
points of fracture (Fig. 263) and the nearer gage mark is 3 ; 
or in other words, that there are 3 spaces on the shorter portion 
of the specimen between the point of rupture and the gage mark 
B. Then the total length to compare with the original is to 
be measured on the broken test-piece from the point 5 to B on the 
right (corresponding to 3 spaces), plus from 4 to 5 on the right, 



3C 



Fig. 263. — Test-piece (Round Bar) after Rupture. 

plus the distance from B to 4 on the left. The sum of these 
lengths will be the " equivalent " total, length after rupture. 
In general terms the method may be stated that if the length 
between gage marks has been divided into x equal spaces and y 
is the nearest number of these spaces on the shorter portion 
between the point of rupture and the gage mark, then mark 
two points M and N on the longer portion, which are y and l/2x 
spaces, respectively, from the fracture. Place the two portions 
of the specimen as closely together as possible and measure from 
the gage mark in the short portion to the mark M. This distance, 
added to double the distance from M to N, gives the required total 
length after rupture. In this way the elongation of the " stand- 
ard " length (x spaces) will be obtained, as if the fracture had 
occurred midway between the gage marks. 

Specifications are often made to require that the fracture 
shall be within the " middle third of the length." 

Detailed Method for Tension Tests. A standard test-piece 
to be tested in tension should be without flaws or cracks, and 
furthermore the material should be monogeneous. Before 



384 POWER PLANT TESTING 

putting it into the testing machine it should be carefully meas- 
ured. With a scriber or scratch the marks indicating one-inch 
divisions should be made with the " laying-off " gage. (Fig. 
262). Very light punch marks may then be made at each of 
the division marks accurately along the axis of the bar. 1 At 
each of these punch marks the diameter of the cross-section 
should be carefully measured with a micrometer caliper to 
thousandths of an inch. The outside punch marks, called the 
"gage marks," are often made a little heavier than the others, 
so that if an extensometer of the type illustrated in Fig. 257 
is used, one of the thumbscrews supporting the clamps at 
each end can be set accurately but lightly into these marks. In 
this position the extensometer will measure accurately the 
elongation of the specimen between the gage marks. The 
testing machine to be used should then be balanced by adjusting 
the counterpoise provided for this purpose. It should be 
observed also that the " check nuts " rest loosely on the table. 
As the load is increased, however, these nuts should be screwed 
down a little from time to time so that if the load is suddenly 
removed when the test-piece breaks, or should happen to slip 
out of the jaws or wedges holding it in place, the jar on the 
machine will be very much relieved. 

After balancing the machine the test-piece should be placed 
carefully and vertically between the " jaws " or wedges in both 
the upper and lower heads, and the extensometer should be 
put in position if one is to be used. Start the machine at a low 
rate of speed till a load of about 1000 to 2000 pounds is indicated 
before taking any measurements of elongation. This first load 
is applied for the purpose of permitting the test-piece to assume 
a true central position, to allow for some slight slipping of the 
test-piece in the jaws before it becomes firmly gripped, and also 
to allow for possible irregularity in the adjustment of the exten- 
someter or similar auxiliary apparatus. After this light load 
has been reached, during which time, doubtless for the kind of 
materials ordinarily tested, there will have been only a very 
small elongation, the load should be applied continuously and 

1 Punch marks can be made accurately along the axis of a round 
bar by putting them at the " scratch " marks made with a scriber an 
inch apart along the length of the test-piece on the reflection of a " beam 
of light " on the bright surface of the test-piece. 



TESTING THE STRENGTH OF MATERIALS 385 

uniformly until the test-piece breaks, stopping only long enough, 
at the required intervals, to make the necessary observations of 
elongation and change of shape of the cross-section when 
" necking " begins. Increments of load are usually determined 
by taking one-tenth * the product obtained by multiplying the 
approximate estimated elastic limit of the material in pounds 
per square inch by the area of the cross-section in square inches. 

Near the elastic limit it is often found desirable to take 
observations at intervals of 500 pounds up to the yield point, 
where suddenly the rate of elongation increases very rapidly. 
By taking these observations at very close intervals at the 
elastic limit, data are secured which make the curves to be 
plotted much more satisfactory. 

In a standard test the stress, that is, the load, must never 
be decreased any appreciable amount when it is intended to 
apply again later an increased load. A stress once applied must 
be maintained or increased continuously till the end of the test. 
Extensometers or other apparatus of delicate construction 
used for measuring the elongation should be removed from the 
test-piece before the specimen is broken. It is customary to 
take off such apparatuses just after the elastic limit is reached; 
although, as a rule, they can be left in place relatively longer 
for materials that are ductile than for those that are hard and 
brittle. Micrometers used on extensometers provided with 
electrical connections are to be set for readings on one side at 
a time, advancing the screw device until the bell rings, indicating 
that the contact has been made. Then turn it back just enough 
to stop the ringing of the bell, and advance the screw on the 
other side till the bell rings again. After also turning back 
the micrometer screws just enough to stop the ringing, observa- 
tions should be taken on both micrometers. Considerable time 
can be saved if, while these observations are being taken, the 
attendant having charge of the machine is meanwhile slowly 
advancing the load. The scale beam should be kept " floating " 
at all times during a test. Never run the balancing poise out 
on the scale beam beyond the point necessary to balance the 

1 In practice the increments of load in commercial tests are often one- 
half or one-third of the load at the elastic limit. For laboratory investi- 
gations it is not unusual to make the increments as small as one-twen- 
tieth of this load. 



386 POWER PLANT TESTING 

beam. If the scale beam is carefully kept " floating " a point 
will be observed at from 50 to 7 5 per cent of the maximum load 
where the scale beam will fall, indicating apparently that it 
has been advanced too far. This point is called the yield point. 
It is defined as the stress at which the rate of elongation suddenly 
and rapidly increases. 

Beyond the elastic limit, when the extensometer has been 
removed, the rate of elongation can be measured with consider- 
able accuracy by means of a large machinist's dividers, with 
the points set accurately on the " gage marks " at the ends of 
the standard length. 

The load when rupture occurs is not usually the maximum. 
When, therefore, considerable " necking " effect is observed, 
the poise on the scale beam should be watched closely and 
when the maximum load has been reached, indicated by the 
falling of the scale beam, this weight should be quickly observed 
and recorded and then the poise should be brought back to 
follow the decreasing load. It will be observed that this part of 
the work is very interesting if it is done carefully. 

After the test-piece has been broken, stop the machine, 
remove the test-piece, clean and return the jaws or wedges to 
their proper places, and leave the machine in good order. 

The broken ends of the test-piece should be joined carefully 
and the length between each of the marks which were originally 
one inch apart should be measured. Check the sum of these 
lengths with the overall length between the gage marks. With a 
micrometer, or preferably a vernier caliper, measure as accurately 
as possible the diameter of the smallest area at the fracture. The 
fracture should be carefully examined to observe whether it is 
fibrous, granular or crystalline; whether coarse, fine or "silky," 
whether cup-shaped, half-cup, or irregular in shape. 

Curves and Calculations. Plot a curve with elongation per 
inch of length (" strain ") as abscissas and stress in pounds per 
square inch as ordinates. This is the familiar " stress-strain " 
diagram. 

Determine from the data obtained the modulus of elasticity 
(E), 1 the elastic limit, the maximum stress, the ultimate stress, 

1 The modulus of elasticity can be determined also from the " stress- 
strain " diagram by calculating the value of the tangent for the angle 
between a line drawn through the origin parallel to the straight part of 



TESTING THE STRENGTH OF MATERIALS 387 

per cent elongation in 8 inches, percentage elongation in 2 inches 
at the fracture, and percentage reduction in area at the fracture. 
Plot a curve of elongation per inch, using for abscissas 1 
the original length in inches and for ordinates the elongations 
measured for each inch between the gage marks. 

Report of Tension Tests 

1. Date, and names of observers 

2. Material to be tested — specification 

3 . Makers and brand of material 

4. Length between principal punch marks, before test 

5. Length between principal punch marks, after test 

6. Average width of test-piece, before test (6 readings) : 

7. Average width of test-piece, after test (6 readings) 

8. Average thickness of test-piece, before test (9 readings) 

9. Average thickness of test-piece after test (6 readings) 

Readings to be taken, for observations 10 and 11 for increments of 

2000 lbs. on scale beam until an elongation of 0.04 in. is obtained 
between readings and then by increments of 1000 lbs. until 
elongation of 0.03 in. is obtained between readings, and finally 
by 500 lbs. until piece nears point of maximum strength, when 
readings should be taken as frequently as possible, keeping beam 
balanced all the time. 

10. Total pull in pounds as shown by the machine 

1 1 . Corresponding total elongation in piece in inches 

12. Yield point, pounds total (elastic limit) 

13. Maximum load, pounds total 

14. Breaking load, pounds total 

15. Character of fracture, description and sketch 

The following results are to be computed : 

16. Original cross-section, sq.in 

17. Final cross-section, sq.in 

18. Reduction in area in sq.in., and in per cent of original area 

19. Final elongation, total and per cent 

20. Stress (pounds per square inch of original area) at elastic limit, maxi- 

mum load and breaking load. 

Tests in Compression. When a specimen of which the length 
is less than five times the smallest dimension is subjected to a 
load producing compression, it fails usually by crushing. Longer 
specimens fail usually by bending toward the side of least resist- 

" stress-strain " curve, reading the scales of co-ordinates, of course, in 
the units of stress and elongation marked on the diagram. It is obvious 
that the value of the tangent of the angle in this case is the unit stress 
divided by the unit elongation, which is, by definition, the modulus of 
elasticity. 

1 If on the curve sheet the " inch marks " on the test-piece are indi- 
cated by equal divisions on the scale of abscissas, then the points showing 
elongation for each inch should be plotted midway between the division 
lines indicating the position of the " inch marks." 



388 POWER PLANT TESTING 

ance. Two general classes of materials are frequently tested 
in compression: (i) Brittle materials, like brick, stone, wood, 
cement, cast iron, etc., which fail usually by shearing, and (2) 
plastic materials, like soft steel, wrought iron, copper, etc., 
which fail usually by a " flowing " of the metal. Because 
of the difficulty in measuring the deformations of short speci- 
mens of the plastic materials, and because the elastic limit in 
tension is invariably practically the same as in compression, 
these plastic materials are not often subjected to compressive 
loads. Methods to be explained here apply, therefore, par- 
ticularly to materials like wood, brick, stone, and cast iron. 

Detailed Method for Compression Tests of Short Test-pieces. 
Specimens of stone, cement, wood, or brick, of which the length 
is less than five times the smallest dimension, are usually pro- 
vided in forms approximately cubes, although brick and wood 
are as often tested in the form of parallelopipeds similar to 
ordinary commercial bricks. Bearing surfaces of specimens 
of stone, brick, and cement should be made as nearly flat and 
parallel as possible, and should then be covered with a thin layer 
of plaster of Paris. Sized paper in thin sheets should be placed 
on the bearing surfaces between the specimen and the plaster 
to prevent the absorption of water from the latter. In order 
to have the plaster set in a true surface the specimen is placed 
between the " heads " of the testing machine for about ten 
minutes after the movable cross-head (B, Fig. 256) has been 
lowered to press lightly on the plaster. For tests in compression 
the test-piece is placed on the table T and the load is applied 
by lowering the movable cross-head B. 

Dimensions of test-pieces must be carefully measured and 
recorded before they are put into the testing machine; and, if 
any of them require the application of plaster of Paris, then the 
measurements must be made before the plaster is put on. After 
balancing the testing machine by means of the counterweight 
with the test-piece on the table, apply the load continuously 
until the specimen is fractured ; or in the case of plastic materials 
till the deformation is quite noticeable. In general conduct 
the test in the same way as for tension, * except that the specimen 

1 Measurements of the amount of compression (shortening) of the 
test-piece cannot be made directly, but must be made between points 
on the heads of the testing machine. If there is likely to be much 



TESTING THE STRENGTH OF MATERIALS 389 

is compressed instead of being stretched. If the material tested 
is cast iron or even hard stone or brick, precautions must be 
taken to protect persons near the machine from flying fragments. 
If the specimen begins to spall or flake off before it breaks down, 
the load corresponding as well as similar information should 
be recorded and placed in the tabulated report under ' ' Remarks. ' ' 
Usually the specimen breaks down suddenly and the interior 
cone or pyramid in stone, brick, cement, and cast iron will be 
plainly seen if the load has been " fairly " applied. In the 
case of tests of wood, this phenomenon will not be observed, but 
the lines of cleavage will usually show clearly a constant angle 
of shearing. 

Detailed Method of Compression Tests of Long Pieces 
(Columns). When the length of a specimen to be tested in 
compression is greater than, at the most, ten times its least 
dimension, it fails invariably by bending toward the side of 
least resistance. The condition of the ends of such test-pieces 
should be as nearly as possible either fixed or perfectly free 
to turn. Either condition is, however, difficult to obtain. 
For test-pieces from 1 5 to 20 inches long usually an extensometer 
may be connected up to read the compression or shortening of 
the test-piece, if it is desired. 1 The observations will be taken 
in the same general way as for tension tests except that now the 
micrometer screws on the extensometer will approach each other, 
so that these screws must be turned back after taking a measure- 
ment by an amount greater than the compression that will be 
produced by the next increment of load. 

yielding of the parts of the machine, the moving head should be lowered 
till its steel " compression plate " presses on the corresponding steel 
block on the table or lower platform with a force of about 1000 pounds. 
Now measure with micrometers the distance between the points on the 
two heads used for compression measurements, first with the load of 
1000 pounds and then with additional increments of 1000 pounds up to 
considerably above the breaking load of the material to be tested. From 
these data a correction curve should be plotted with which to correct 
the deflections observed when the specimen is tested. 

When blocks of wood are to be tested in compression, readings of the 
micrometers should not be taken till a pressure of 500 to 1000 pounds 
per square inch has been applied. This load will be required to crush 
the rough fibers. 

1 The lateral deflection along the neutral plane is sometimes deter- 
mined by stretching a fine wire along the length of the specimen parallel 
to the neutral axis. 



390 



POWER PLANT TESTING 



Report on Compression Tests 

i . Date and names of observers , 

2. Kind of material 

3. Average thickness of test-piece (4 readings), inches 

4. Average width of test-piece (4 readings), inches 

Machine is to be started and kept running continuously until fracture 
takes place, the beam being kept balanced carefully all the time. Read- 
ings to be taken, and calculations made therefrom as follows: In making 
these tests, wood and brick will be used and two pieces of each kind are 
to be tested, with each kind of stress. 











Kind of Wood 


White Pine. 


Yellow Pine. 


Bricks 








1 


2 


1 


2 


1 








Scale reading in pounds at 














Character of fracture, sketch. 
Cross-section from items 3 

and 4, square inches 

Breaking stress lbs. per square 

inch for each piece 

Average breaking stress for 

each kind of wood 

Modulus of elasticity, lbs. per 

square inches 





Sketches, Curves, and Calculations. Sketch the character 
of the fracture for each specimen tested, indicating, for wood, 
the direction of the grain. Previously, the original shape of 
the specimen should have been sketched and dimensioned. 

Calculate the maximum unit stress. 

If the material was suitable for the measurement of compres- 
sion, plot "stress-strain" diagrams, and calculate the modulus 
of elasticity. 

Transverse Bending Tests. The most common test by 
transverse or cross-bending is that of a beam usually of either 
wood or steel, of which the coefficient of elasticity and the 
" elastic curve " are desired. Deflections of such beams give 
the data needed. Such tests may be made with a testing 
machine like the one shown in Fig. 256, which is provided with 
supporting abutments marked in the figure UU', and by insert- 
ing into the movable head the attachment for applying the load 



TESTING THE STRENGTH OF MATERIALS 



391 



along a line across the beam rather than on a comparatively 
large area as in the tests already described when the load was 
applied directly by the flat surface of the cross-head B. Special 
transverse testing machines are, however, sometimes available. 
A machine of this kind is illustrated in Fig. 264. 

In the case of a wooden beam to be tested by loading at the 
middle, a fine steel wire should be stretched between two pins 




Fig. 264. — Machine for Transverse Tests. 

located as accurately as possible above the points of support and 
on the line of intersection of the neutral plane with the side of 
the beam. The wire should be fastened to one of these pins and 
allowed to hang over the other, being kept taut by means of 
a weight . attached to the free end, Fig. 265. A steel scale, 
preferably highly polished so that it will show the image of the 
wire, should be attached in any suitable way to the side of the 



392 



POWER PLANT TESTING 



beam, so that the edge along which the scale readings to be 
observed are marked will be exactly half-way between the two 
supports. The beam must be protected from indentation by 
the knife-edges by small bearing plates. The load should be 
applied centrally in increments to give approximately 7 V inch 
deflections to the elastic limit, and beyond to give deflections of 
approximately £j inch. If it can be done successively, the 
deflections should be read without stopping the test; unless, 
of course, the permanent set is to be determined, when after 
each increment, the beam must be released from its load. 



Fig. 265. — Device for Measuring the Deflection of a Wooden Beam. 

Curves and Calculations. Plot a curve taking the load 
applied in pounds for abscissas and deflections in inches for 
ordinates. 

Sketch the character of the fracture. 

Calculate the modulus of elasticity, 1 the modulus of rupture, 
and the stress in the outer fiber at the elastic limit from the 
curve. 

1 The modulus of elasticity is calculated by the formula 

- 4 is «> 

The modulus of rupture from 

w„lc 

'«=7P • • (I24) 

and the stress in the outer fiber at the elastic limit by 

Wplc 

f -=rr (,25) 

"whenw e =load at the elastic limit in pounds per square inch; 

w M =load at the point of rupture in pounds per square inch; 
1 = length of beam (span) in inches ; 
d = deflection in inches ; 

c = distance from the neutral axis to the outer fiber in inches; 
I=moment of inertia, inches. 



TESTING THE STRENGTH OF MATERIALS 393 

Torsion Tests are made to determine the strength of a 
material to resist twisting forces. A typical machine for such 
tests is illustrated in Fig. 266. It consists in its essential parts 
of the frame FF', the " jaw " heads A and B for gripping the 
rod R to be tested, and the system of weighing levers on which 
the poise P is balanced. The load is applied to the rod R by 
power through the gears shown connected to the head B. 

The power is applied by means of the pulley and gears shown 
at the right-hand side, or may be applied by hand power 
by turning hand wheels. With hand power usually more 
satisfactory results can be obtained than with power applied 




Fig. 266. — Riehle Torsion Testing Machine. 

mechanically, because the rate of twisting can be more closely 
regulated. The amount of twist or the angular deformation 
is indicated by index-arms connected to opposite ends of the 
test-piece. 

An autographic torsion testing machine operated by hand 
power by means of the crank is sometimes used. The move- 
ment of the crank tends to rotate the test-piece which at the 
opposite end of the machine is fastened to a pendulum carrying 
a heavy bob. The resistance of the pendulum and its weight 
measure the power applied, which is equal to the length of the 
lever arm times the sine of the angle of inclination times the 
constant weight of the bob. 



394 POWER PLANT TESTING 

Tests are made usually by increasing the twisting moment 
by increments of about 200 inch-pounds, 1 measuring for each 
increment the torsion angle. 

Curves and Calculations. Plot a curve, using torsion angle 
for abscissas and twisting moment for ordinates. Calculate 
from this curve the' unit stresses 2 (shearing) at the elastic limit, 
at the point of rupture, and also the maximum value of stress. 
Determine the torsion angle at the elastic limit and at the point of 
rupture, the helix angles, 3 and the modulus of elasticity for torsion. 4 

Impact Tests. Materials are tested by impact, usually by 
striking a test-piece with a weight allowed to fall upon it. 
Metals used in the manufacture of machinery and in railroad 
construction where it is likely to be subjected to shocks and 
blows are in many cases tested to determine the effect of the 
impact due to a blow. 

Some testing machines for such tests are made like a pile- 
driver with the weight dropping vertically from a sort of gallows 
upon the test-piece. A more common form, however, of such 
machines consists of a pendulum provided with a heavy bob 

1 If tests are made of large sections of high-grade material, like, for 
example, a shaft of nickel steel for a students' class, it is expensive to 
break many specimens, so that for this reason the twisting moment pro- 
ducing a maximum stress just inside the elastic limit is computed before 
making the test, and this value is not to be exceeded. 

2 The unit stress is calculated with the formula: 

M / f s = V c > or f s = Mc/l 2 „ .... (126) 

where M is the torsional moment in inch-pounds, c is distance in inches 
from the neutral axis to the extreme fiber, and I p is the polar movement 
of inertia. When c=r (the radius) as in the case of a cylindrical test- 
piece, I p = ^tzt*. 

3 Torsion produces a peculiar arrangement of the outer fibers in the 
form of helices, as observed in broken test-pieces. Each one of these 
fibers makes an angle with its original position equal to its angular dis- 
tortion a. Any particle on the surface is also moved through an angle 
/?, having its vertex in the axis and in a plane perpendicular to the axis. 
Now if we neglect the functions of small angles, we can write approxi- 
mately la =r/?, where 1 is the effective length of the test-piece and r is 
the radius. The helix-angle a =r/?/l. 

* The modulus of elasticity in torsion ("modulus of rigidity"), 

Es=f s -4- a, 

as above, then 

K.--. .......... daw 



TESTING THE STRENGTH OF MATERIALS 395 

intended for delivering a blow on the middle of a test-piece in 
the shape of a bar, preferably of a rectangular section, held on 
two knife-edge supports attached to a heavy bedplate. Such 
machines are particularly designed for comparative tests of cast 
iron. They are provided with an arc concentric with the move- 
ment of the bob of the pendulum, graduated to read the verti- 
cal fall of the bob in feet. A tripping device is attached to the 
side of the graduated arc for permitting the bob to be supported 
and then dropped from any height within the limits of the 
machine. Since the deflection is very small, a device is usually 
supplied for magnifying it, and by means of a pencil-point 
traveling over a chart an autographic record is made of the 
deflections for each blow delivered by the bob. With such 
instruments the rebound of the test-piece and its permanent 
set must be carefully excluded from the measured deflection. 
One way to do this is to draw a " zero line " with the test- 
piece in place but before a blow is struck. Deflections and 
permanent set will then be measured on one side of this line 
and " rebounds " on the other. 

To determine the center load to be applied that will be 
equivalent to the impact, the following symbols are used: 

Let Wi = weight of the bob in pounds; 

h = the vertical distance it falls, in feet ; 
w 2 = the equivalent maximum center load, in pounds, and 
d = the deflection in feet, then 



Wih = ^w 2 d, 

2W 5 h 



(128) 



With this value of w 2 the usual properties of the material may be 
calculated by formulas (123), (124) and (125), page 392. 

Cement Tests. Cements are tested usually for tensile and 
crushing strength, for fineness, and for the time required for 
" setting." Tests for crushing strength (compression) are 
usually made by crushing cubical blocks in a testing machine 
designed for general tension and compression tests (see page 378) . 
For tensile tests, however, special machines, designed particularly 
for testing cement, are generally used. Because of the nature 
of the material it is absolutely necessary that the power is 



396 



POWER PLANT TESTING 



applied in the line of the axis of the test-piece and also with 
steadiness and in increments as uniform as possible. There is 
a standard size and shape for test-pieces of cement, and they 
must be made in a certain prescribed way in order that different 
tests may be compared. The standard briquette for testing 




Fig. 267. — Standard Specimen for Cement. 

(one square inch section) is shown in Fig. 267, and Fig. 268, 
shows moulds suitable for making the test-pieces or briquettes, 
as they are called. 

Cement-testing machines are invariably provided with moulds 
for making standard briquettes. These moulds are divided 






Fig. 268. — Cement Moulds and Briquettes. 



along a longitudinal center line into two halves which, when 
placed together, fit closely and are held in place by means of 
pins, or dowels, preventing endwise movement, and by clamps 
pressing together the two parts of the mould. The strength 



TESTING THE STRENGTH OF MATERIALS 397 

of the briquettes is affected by the time allowed for hardening, 
the amount of water used, and by the method of mixing the 
cement. (See page 400.) 

Power is applied in the automatic cement-testing machine 
shown in Fig. 269, by shot dropped from a cylindrical hopper 
into a pail supported on a scales. The briquette of cement 




Fig. 269. — Automatic Cement Testing Machine. 

being tested is held between two shackles or " holders " con- 
nected to a hand wheel used to regulate the distance between 
the shackles. When a briquette breaks the scale beam drops 
and closes automatically a valve, stopping the delivery of shot 
into the pail. The operation of the machine may be described 
briefly as follows : Hang the hopper on the hook as shown and 
put enough shot into it to balance the counterpoise. Now 



398 



POWER PLANT TESTING 



put the briquette into the shackles and adjust the hand wheel 
so that the scale beam will rise nearly to the stop. When the 
valve is opened shot will begin to fall into the pail. The deliv- 
ery of the shot into the pail should be slow. When the bri- 
quette has broken, the scale beam has dropped and the valve 




Fig. 2' 



-Hand-operated Cement T 



has been closed. The weight of shot collected in the pail shows 
the number of pounds required to break the briquette. 

A non-automatic type of cement-testing machine is illus- 
trated in Fig. 270. In this machine the power is applied by 
moving a hand wheel operating by means of a screw the 
system of levers transmitting the load to the briquette in the 



TESTING THE STRENGTH OF MATERIALS 399 

shackles. The tension produced by this load may obviously 
be balanced by weights applied to the scale beam above. In 
order to secure a very uniform and slow movement of the 
poise it is carried along the scale beam by a cord moved by a 
small crank. In applying the load the hand wheel should be 
moved as slowly and uniformly as possible to avoid a jerking 
motion. In the figure one of the standard briquette moulds, 
and a tray used for immersing the briquettes in water after they 
have set are shown. Fig. 271 shows the proper position of the 
briquette in the supporting shackles. 

Test of Cement for Fineness is made by determining the 
amount by weight of a given sample that will not pass through 
sieves with meshes of a standard size. The 
American Society of Civil Engineers recommends 
the use of sieves of 2500, 5476 and 10,000 
meshes per square inch. Sieves with approxi- 
mately these meshings are known as Nos. 50, 
80, and 100. A weighed sample of cement is 
first passed through No. 50 sieve and the weight 
of that remaining in the sieve is recorded. That 
passing through is then put into the next sieve 
(No. 80) and the residue in this sieve is likewise 
weighed, while that passing through goes to 
the finest sieve (No. ico). Results of this 
test for fineness are expressed by the per- FlG 

centages that the various residues remaining 
in the sieves are of the original weight of the sample. 

Unless cement is ground as fine as flour it has very little 
" binding power." The coarse particles are nearly as inert for 
" cementing " as sand. 

Test of Cement for Time of Setting is made by mixing on a 
slab of glass circular pats about 3 inches in diameter and one- 
half inch thick. Then when a blunt needle (one-twelfth inch 
in diameter as the point) and loaded with a weight of one- 
quarter pound " ceases to penetrate the entire mass setting is 
said to have begun." Similarly when a needle one twenty- 
fourth inch in diameter loaded with a weight of one pound 
ceases to penetrate at all, setting is said to be ended. 

Making Briquettes. Neat Cement. Before filling moulds 
with cement they should be carefully cleaned and rubbed on the 




400 POWER PLANT TESTING 

inside surface with a rag saturated with kerosene. Then clamp 
the parts together, placing the moulds preferably on a large 
slab of glass, or a similar material providing a plane surface 
which will not absorb moisture from the briquettes. A quantity 
of cement, enough to fill several moulds, should now be mixed 
with water (usually not as much as 25 per cent by weight) to 
make a rather stiff but very plastic and homogeneous mixture. 
It should be " worked " for at least three minutes. Put this 
mixture into moulds, pressing it down firmly, especially around 
the sides, preferably with the thumbs, in order that the pressure 
exerted will not be excessive. Level the surfaces of the briquettes 
with a trowel, being careful that in this operation too much 
is not taken from the middle so as to make the briquettes of 
unequal thickness. Usually cement briquettes are not tested 
in tension until several days after they have been made, and 
in that case the moulds with the briquettes in them should 
be allowed to remain on a slab which will not absorb moisture 
from them for twenty-four hours, in an atmosphere which is not 
very dry. After that time the briquettes should be carefully 
removed from the moulds, put into a suitable tray, like the one 
shown in Fig. 270, and immersed in a tank containing water. 1 
Near one of the ends, each briquette should be marked with 
significant numbers or letters, so that the maker and the date 
of making will not be confused. The cement must not, of course, 
be permitted to begin to set before it is put into the moulds. 

Mortar Briquettes for testing are made usually of five, two, 
or three parts of sand to one part of cement. The sand to be used 
is to be approximately of such fineness that it will all pass 
through a No. 20 sieve and is all held on a No. 30 sieve. Mortar 
briquettes for standard tests are made of pure crushed quartz of 
the kind used in the manufacture of sandpaper. For mortar 
briquettes less water will be needed than for those of neat 
(" pure ") cement. The mortar briquettes should be worked 
with the trowel for at least four minutes. Moulds should be 
well filled with the mortar, which should then be pressed down 
to a flat surface with the trowel. The briquettes are to be set 
aside and later immersed in water as specified for those of neat 
cement. 

1 The water in this tank should be changed once in seven days, and 
should be kept at normal " room " temperatures. 



TESTING THE STRENGTH OF MATERIALS 



401 



For laboratory tests, usually after seven days, or else after 
twenty-eight days, the briquettes are taken from the water and 
placed in a cement-testing machine for testing in tension. Apply 
the load at as uniform a rate as possible, without jerks, and if a 
non-automatic machine is used the scale beam must be kept 
" floating " all the time, so that when the briquette breaks the 
correct load will be indicated by the position of the poise on the 
scale beam. In some laboratories it is recommended that pieces 
of thin rubber bands be inserted between the edges of the shack- 
les or " holders " and the briquette, as in this way it is claimed 
there is greater certainty of having it break at the middle, that 
is, in the smallest section where the area is supposedly exactly 
one square inch. 

Data regarding tests of neat cement and mortar briquettes 
should be tabulated in a form similar to the following : 

Form for Cement Tests 



i. Date, and names of observers. 

2. Name and kind of cement. 

3. Makers and location of plant. 

4. Distinguishing mark on briquettes. 

5. Date of mixing and time. 

6. Temperature of room at time of mixing, deg. F. 

7. Temperature of water at time of mixing, deg. F. 

8. Conditions of setting: as to time briquettes were left in dampened air before immersion, 

etc. 

9. Activity of the cement or time of initial and final setting. 1 
10. Fineness of grinding. 





Kind of Briquette. 


Neat. 


Sand. 


12 


Composition 

of 

Briquettes. 


Per Cent of Cement 

Per Cent of Water 


Per Cent of Cement 

Per Cent of Water 




Per Cent of San 


1. . 










No. of Briquettes. 


7 Day. 


28 Day. 


Remarks 


7 Day. 


28 Day, 






1 


— 


3 


4 


S 


— 


7 


— 


1 


2 


3 


4 


S 


— 


7 


8 




is 
16 

17 
18 


Time of test. 

Breaking Strength, 
lbs. 

Appearance of frac- 
ture — give sketch 
of each here. 

Temp, of Room at 
time of test. deg.F. 









In reporting the results of these experiments it is important that the effect of different 
percentages of water, sand, etc., and time of immersion, be fully discussed. 

1 The time between the end mixing and the successful resistance to penetration of 
the needle ■}., inch in diameter with \ pound weight is called the "time of initial setting." 
Similarly, the time elapsing between the end of mixing and the resistance to penetration 
of the needle = V inch in diameter with 1 pound weight is called the " time of final setting." 



APPENDIX 



Two sets of tables which the author has found useful for 
"rough and ready" calculations are given on the following 
pages. Table I is a short table of the more important prop- 
erties of saturated steam. This table has been taken with 
permission from Allen and Bursley's Heat Engines. 

Table II gives for various common substances the specific 
gravity, density (weight per cubic foot), specific heat and 
coefficients of expansion per degree Fahrenheit, both linear and 
volumetric. Coefficient of volumetric expansion is three times 
the linear coefficient of expansion. 

TABLE I 

Properties of Saturated Steam 
english units 



go,. 


h 

1! 


13 


14 

1h' B 


2s 


sa]h 


ill 




fjfc 


*Q 


n 


■3*8 


Eh° 


O 


£± 


•<* 


V 


t 


h 


L 


H 


V 


s 


p 


.0886 


32 





1072.6 


1072.6 


3301.0 


.000303 


.0886 


.2562 


60 


28.1 


1057.4 


1085.5 


1207.5 


.000828 


.2562 


.5056 


80 


48.1 


1046.6 


1094.7 


635.4 


.001573 


.5056 


1 


101.8 


69.8 


1034.6 


1104.4 


333.00 


.00300 


1 


2 


126.1 


94.1 


1021.4 


1115.5 


173.30 


.00577 


2 


3 


141.5 


109.5 


1012.3 


1121.8 


118.50 


.00845 


3 


4 


153.0 


120.9 


1005.6 


1126.5 


90.50 


.01106 


4 


5 


162.3 


130.2 


1000.2 


1130.4 


73.33 


.01364 


5 


6 


170.1 


138.0 


995.7 


1133.7 


61.89 


.01616 


6 


7 


176.8 


144.8 


991.6 


1136.4 


53.58 


.01867 


7 


8 


182.9 


150.8 


988.0 


1138.8 


47.27 


.02115 


8 



403 



404 



POWER PLANT TESTING 



Properties op Saturated Steam 
english units 



Continued 



w °" d 

to 3 c 
3* 


IS 


n 


[So 
■p s o 

a >-s 
Jo 


g a 

"30Q 

g-s 


$£ 6 to 


Ha 

0h 


3 p 


p 


t 


h 


L 


H 


V 


1 


p 


9 


188.3 


156.3 


984.8 


1141.1 


42.36 


.02361 


9 


10 


193.2 


161.2 


981.7 


1142.9 


38.38 


.02606 


10 


11 


197.7 


165.8 


978.9 


1144.7 


35.10 


.02849 


11 


12 


202.0 


170.0 


976.3 


1146.3 


32.38 


.03089 


12 


13 


205.9 


173.9 


973.9 


1147.8 


30.04 


.03329 


13 


14 


209.6 


177.6 


971.6 


1149.2 


28.02 


.03568 


14 


14.7 


212.0 


180.1 


970.0 


1150.1 


26.79 


.03733 


14.7 


15 


213.0 


181.1 


969.4 


1150.5 


26.27 


.03806 


15 


16 


216.3 


184.5 


967.3 


1151.8 


24.77 


.04042 


16 


17 


219.4 


187.7 


965.3 


1153.0 


23.38 


.04277 


17 


18 


222.4 


190.6 


963.4 


1154.0 


22.16 


.04512 


18 


19 


225.2 


193.5' 


961.5 


1155.0 


21.07 


.04746 


19 


20 


228.0 


196.2 


959.7 


1155.9 


20.08 


.04980 


20 


21 


230.6 


198.9 


958.0 


1156.9 


19.18 


.05213 


21 


22 


233.1 


201.4 


956.4 


1157.8 


18.37 


.05445 


22 


23 


235.5 


203.9 


954.8 


1158.7 


17.62 


.05676 


23 


24 


237.8 


206.2 


953.2 


1159.4 


16.93 


.05907 


24 


25 


240.1 


208.5 


951.7 ' 


1160.2 


16.30 


.0614 


25 


26 


242.2 


210.7 


950.3 


1161.0 


15.71 


.0636 


26 


27 


244.4 


212.8 


948.9 


1161.7 


15.18 


.0659 


27 


28 


246.4 


214.9 


947.5 


1162.4 


14.67 


.0682 


28 


29 


248.4 


217.0 


946.1 


1163.1 


14.19 


.0705 


29 


30 


250.3 


218.9 


944.8 


1163.7 


13.74 


.0728 


30 


31 


252.2 


220.8 


943.5 


1164.3 


13.32 


.0751 


31 


32 


254.1 


222.7 


942.2 


1164.9 


12.93 


.0773 


32 


33 


255.8 


224.5 


941.0 


1165.5 


12.57 


.0795 


33 


34 


257.6 


226.3 


939.8 


1166.1 


12.22 


.0818 


34 


35 


259.3 


228.0 


938.6 


1166.6 


11.89 


.0841 


35 


36 


261.0 


229.7 


937.4 


1167.1 


11.58 


.0863 


36 


37 


262.6 


231.4 


936.3 


1167.7 


11.29 


.0886 


37 


38 


264.2 


233.0 


935.2 


1168.2 


11.01 


.0908 


38 


39 


265.8 


234.6 


934.1 


1168.7 


10.74 


.0931 


39 


40 


267.3 


236.2 


933.0 


1169.2 


10.49 


.0953 


40 


41 


268.7 


237.7 


931.9 


1169.6 


10.25 


.0976 


41 


42 


270.2 


239.2 


930.9 


1170.1 


10.02 


.0998 


42 


43 


271.7 


240.6 


929.9 


1170.5 


9.80 


.1020 


43 


44 


273.1 


242.1 


928.9 


1171.0 


9.59 


.1043 


44 


45 


274.5 


243.5 


927.9 


1171.4 


9.39 


.1065 


45 


46 


275.8 


244.9 


926.9 


1171.8 


9.20 


.1087 


46 



APPENDIX 



405 



Properties op Saturated Steam — Continued 

ENGLISH UNITS 





IX 


"o 3 

+> cr 

ffl 


*s o 


la 

Kg 
H ° 


II s ! 

m> 6 


Sid 


1!« 


P 


* 


h 


L 


H 


V 


1 


P 


47 


277.2. 


246.2 


926.0 


1172.2 


9.02 


.1109 


47 


48 


278.5 


247.6 


925.0 


1172.6 


8.84 


.1131 


48 


49 


279.8 


248.9 


924.1 


1173.0 


8.67 


.1153 


49 


50 


281.0 


250.2 


923.2 


1173.4 


8.51 


.1175 


50 


51 


282.3 


251.5 


922.3 


1173.8 


8.35 


.1197 


51 


52 


283.5 


252.8 


921.4 


1174.2 


8.20 


.1219 


52 


53 


284.7 


254.0 


920.5 


1174.5 


8.05 


.1241 


53 


54 


285.9 


255.2 


919.6 


1174.8 


7.91 


.1263 


54 


55 


287.1 


256.4 


918.7 


1175.1 


7.78 


.1285 


. 55 


56 


288.2 


257.6 


917.9 


1175.5 


7.65 


.1307 


56 


57 


289.4 


258.8 


917.1 


1175.9 


7.52 


.1329 


57 


58 


290.5 


259.9 


916.2 


1176.1 


7.40 


.1351 


58 


59 


291.6 


261.1 


915.4 


1176.5 


7.28 


.1373 


59 


60 


292.7 


262.2 


914.6 


1176.8 


' 7.17 


.1394 


60 


61 


293.8 


263.3 


913.8 


1177.1 


7.06 


.1416 


61 


62 


294.9 


264.4 


913.0 


1177.4 


6.95 


.1438 


62 


63 


295.9 


265.5 


912.2 


1177.7 


6.85 


.1460 


63 


64 


297.0 


266.5 


911.5 


1178.0 


6.75 


.1482 


64 


65 


298.0 


267.6 


910.7 


1178.3 


6.65 


.1503 


65 


66 


299.0 


268.6 


910.0 


1178.6 


6.56 


.1525 


66 


67 


300.0 


269.7 


909.2 


1178.9 


6.47 


.1547 


67 


68 


301.0 


270.7 


908.4 


1179.1 


6.38 


.1569 


68 


69 


302.0 


271.7 


907.7 


1179.4 


6.29 


.1591 


69 


70 


302.9 


272.7 


906.9 


1179.6 


6.20 


.1612 


70 


71 


303.9 


273.7 


906.2 


1179.9 


6.12 


.1634 


71 


72 


304.8 


274.6 


905.5 


1180.1 


6.04 


.1656 


72 


73 


305.8 


275.6 


904.8 


1180.4 


5.96 


.1678 


73 


74 


306.7 


276.6 


904.1 


1180.7 


5.89 


.1699 


74 


75 


307.6 


277.5 


903.4 


1180.9 


5.81 


.1721 


75 


76 


308.5 


278.5 


902.7 


1181.2 


5.74 


.1743 


76 


77 


309.4 


279.4 


902.1 


1181.5 


5.67 


.1764 


77 


78 


310.3 


280.3 


901.4 


1181.7 


5.60 


.1786 


78 


79 


311.2 


281.2 


900.7 


1181.9 


5.54 


.1808 


79 


80 


312.0 


282.1 


900.1 


1182.2 


5.47 


.1829 


80 


81 


312.9 


283.0 


899.4 


1182.4 


5.41 


.1851 


81 


82 


313.8 


283.8 


898.8 


1182.6 


5.34 


.1873 


82 


83 


314.6 


284.7 


898.1 


1182.8 


5.28 


.1894 


83 


84 


315.4 


285.6 


897.5 


1183.1 


5.22 


.1915 


84 


85 


316.3 


286.4 


896.9 


1183.3 


5.16 


.1937 


85 



406 



POWER PLANT TESTING 



Properties of Saturated Steam - 
english units 



■ Continued 



fig o- 

■2P4 


(B 


£.2" 

fH 
H 


c3 oj 

CD h 

^ a ci 
•p a o 
a >•$ 

f 
3 o 


la 

I" 8 


as]h 

m> 6 






p 


« 


h 


L 


H 


V 


V 


p 


86 


317.1 


287.3 


896.2 


1183.5 


5.10 


.1959 


86 


87 


317.9 


288.1 


895.6 


1183.7 


5.05 


.1980 


87 


88 


318.7 


288.9 


895.0 


1183.9 


5.00 


.2002 


88 


89 


319.5 


289.8 


894.3 


1184.1 


4.94 


.2024 


89 


90 


320.3 


290.6 


893.7 


1184.3 


4.89 


.2045 


90 


91 


321.1 


291.4 


893.1 


1184.5 


4.84 


.2066 


91 


92 


321.8 


292.2 


892.5 


1184.7 


4.79 


.2088 


92 


93 


322.6 


293.0 


891.9 


1184.9 


4.74 


.2110 


93 


94 


323.4 


293.8 


891.3 


1185.1 


4.69 


.2131 


94 


95 


324.1 


294.5 


890.7 


1185.2 


4.65 


.2152 


95 


96 


324.9 


295.3 


890.1 


1185.4 


4.60 


.2173 


96 


97 


325.6 


296.1 


889.5 


1185.6 


4.56 


.2194 


97 


98 


326.4 


296.8 


889.0 


1185.8 


4.51 


.2215 


98 


99 


327.1 


297.6 


" 888.4 


1186.0 


4.47 


.2237 


99 


100 


327.8 


298.4 


887.8 


1186.2 


4.430 


.2257 


100 


101 


328.6 


299.1 


887.2 


1186.3 


4.389 


.2278 


101 


102 


329.3 


299.8 


886.7 


1186.5 


4.349 


.2299 


102 


103 


330.0 


300.6 


886.1 


1186.7 


4.309 


.2321 


103 


104 


330.7 


301.3 


885.6 


1186.9 


4.270 


.2342 


104 


105 


331.4 


302.0 


885.0 


1187.0 


4.231' 


.2364 


105 


106 


332.0 


302.7 


884.5 


1187.2 


4.193 


.2385 


106 


107 


332.7 


303.4 


883.9 


1187.3 


4.156 


.2407 


107 


108 


333.4 


304.1 


883.4 


1187.5 


4.119 


.2428 


108 


109 


334.1 


304.8 


882.8 


1187.6 


4.082 


.2450 


109 


110 


334.8 


305.5 


882.3 


1187.8 


4.047 


.2472 


110 


111 


335.4 


306.2 


881.8 


1188.0 


4.012 


.2493 


111 


112 


336.1 


306.9 


881.2 


1188.1 


3.977 


.2514 


112 


113 


336.8 


307.6 


880.7 


1188.3 


3.944 


.2535 


113 


114 


337.4 


308.3 


880.2 


1188.5 


3.911 


.2557 


114 


114.7 


337.9 


308.8 


879.8 


1188.6 


3.888 


.2572 


114.7 


115 


338.1 


309.0 


879.7 


1188.7 


3 878 


.2578 


115 


116 


338.7 


309.6 


879.2 


1188.8 


3.846 


.2600 


116 


117 


339.4 


310.3 


878.7 


1189.0 


3.815 


.2621 


117 


118 


340.0 


311.0 


878.2 


1189.2 


3.784 


.2642 


118 


119 


340.6 


311.7 


877.6 


1189.3 


3.754 


.2663 


119 


120 


341.3 


312.3 


877.1 


1189.4 


3.725 


.2684 


120 


121 


341.9 


313.0 


876.6 


1189.6 


3.696 


.2706 


121 


122 


342.5 


313.6 


876.1 


1189.7 


3.667 


.2727 


122 


123 


343.2 


314.3 


875.6 


1189.9 


3.638 


.2749 


123 



APPENDIX 



407 



Properties of Saturated Steam 
english units 



Continued 



h 

§ CO ^ 


-1 


§3 


« 03 

tfi ° - 
" a a 


la 

r°"o 




QgO 




^ 


I s 


K 


£ o 


H 


o 


Pi 


^ 


V 


t 


h 


L 


H 


V 


D 


V 


124 


343.8 


314.9 


875.1 


1190.0 


3.610 


.2770 


124 


125 


344.4 


315.5 


874.6 


1190.1 


3.582 


.2792 


125 


126 


345.0 


316.2 


874.1 


1190.3 


3.555 


.2813 


126 


127 


345.6 


316.8 


873.7 


1190.5 


3.529 


.2834 


127 


128 


346.2 


317.4 


873.2 


1190.6 


3.503 


.2855 


128 


129 


346.8 


318.0 


872.7 


1190.7 


3.477 


.2876 


129 


130 


347.4 


318.6 


872.2 


1190.8 


3.452 


.2897 


130 


131 


348.0 


319.3 


871.7 


1191.0 


3.427 


.2918 


131 


132 


348.5 


319.9 


871.2 


1191.1 


3.402 


.2939 


132 


133 


349.1 


320.5 


870.8 


1191.3 


3.378 


.2960 


133 


134 


349.7 


321.0 


870.4 


1191.4 


3.354 


.2981 


134 


135 


350.3 


321.6 


869.9 


1191.5 


3.331 


.3002 


135 


136 


350.8 


322.2 


869.4 


1191.6 


3.308 


.3023 


136 


137 


351.4 


322.8 


868.9 


1191.7 


3.285 


.3044 


137 


138 


352.0 


323.4 


868.4 


1191.8 


3.263 


.3065 


138 


139 


352.5 


324.0 


868.0 


1192.0 


3.241 


.3086 


139 


140 


353.1 


324.5 


867.6 


1192.1 


3.219 


.3107 


140 


141 


353.6 


325.1 


867.1 


1192.2 


3.198 


.3128 


141 


142 


354.2 


325.7 


866.6 


1192.3 


3.176 


.3149 


142 


143 


354.7 


326.3 


866.2 


1192.5 


3.155 


.3170 


143 


144 


355.3 


326.8 


865.8 


1192.6 


3.134 


.3191 


144 


145 


355.8 


327.4 


865.3 


1192.7 


3.113 


.3212 


145 


146 


356.3 


327.9 


864.9 


1192.8 


3.093 


.3233 


146 


147 


356.9 


328.5 


864.4 


1192.9 


3.073 


.3254 


147 


148 


357.4 


329.0 


864.0 


1193.0 


3.053 


.3275 


148 


149 


357.9 


329.6 


863.5 


1193.1 


3.033 


.3297 


149 


150 


358.5 


330.1 


863.1 


1193.2 


3.013 


.3319 


150 


152 


359.5 


331.2 


862.3 


1193.5 


2.975 


.3361 


152 


154 


360.5 


332.3 


861.4 


1193.7 


2.939 


.3403 


154 


156 


361.6 


333.4 


860.5 


1193.9 


2.903 


.3445 


156 


158 


362.6 


334.4 


859.7 


1194.1 


2.868 


.3487 


158 


160 


363.6 


335.5 


858.8 


1194.3 


2.834 


.3529 


160 


162 


364.6 


336.6 


858.0 


1194.6 


2.801 


.3570 


162 


164 


365.6 


337.6 


857.2 


1194.8 


2.768 


.3613 


164 


166 


366.5 


338.6 


856.4 


1195.0 


2.736 


.3655 


166 


168 


367.5 


339.6 


855.5 


1195.1 


• 2.705 


.3697 


168 


170 


368.5 


340.6 


854.7 


1195.3 


2.674 


.3739 


170 


172 


369.4 


341.6 


. 853.9 


1195.5 


2.644 


.3782 


172 


174 


370.4 


342.5 


853.1 


1195.6 


2.615 


.3824 


174 


176 


371.3 


343.5 


852.3 


1195.8 


2.587 


.3865 


176 



i08 



POWER PLANT TESTING 



Properties of Saturated Steam 
english units 



Concluded 







a> 




§ ■ 
Kg 

r 


<5 ^"d 
"§3i£ 2 


pgd 




$* 


J 5 


K 


►3 o 


H ° 


o 


p-i 


3* 


V 


t 


h 


L 


H 


V 


i 


V 


178 


372.2 


344.5 


851.5 


1196.0 


2.560 


.3907 


178 


180 


373.1 


345.4 


850.8 


1196.2 


2.532 


.3949 


180 


182 


374.0 


346.4 


850.0 


1196.4 


2.506 


.3990 


182 


184 


374.9 


347.4 


849.3 


1196.7 


2.480 


.4032 


184 


186 


375.8 


348.3 


848.5 


1196.8 


2.455 


.4074 


186 


188 


376.7 


349.2 


847.7 


1196.9 


2.430 


.4115 


188 


190 


377.6 


350.1 


847.0 


1197.1 


2.406 


.4157 


190 


192 


378.5 


351.0 


846.2 


1197.2 


2.381 


.4200 


192 


194 


379.3 


351.9 


845.5 


1197.4 


2.358 


.4242 


194 


196 


380.2 


352.8 


844.8 


1197.6 


2.335 


.4284 


196 


198 


381.0 


353.7 


844.0 


1197.7 


2.312 


.4326 - 


198 


200 


381.9 


354.6 


843.3 


1197.9 


2.289 


.4370 


200 


202 


382.7 


355.5 


842.6 


1198.1 


2.268 


.4411 


202 


204 


383.5 


356.4 


841.9 


1198.3 


2.246 


.4452 


204 


206 


384.4 


357.2 


841.2 


1198.4 


2.226 


.4493 


206 


208 


385.2 


358.1 


840.5 


1198.6 


2.206 


.4534 


208 


210 


386.0 


358.9 


839.8 


1198.7 


2.186 


.4575 


210 


212 


386.8 


359.8 


839.1 


1198.9 


2.166 


.4618 


212 


214 


387.6 


360.6 


838.4 


1199.0 


2.147 


.4660 


214 


216 


388.4 


361.4 


837.7 


1199.1 


2.127 


.4700 


216 


218 


389.1 


362.3 


837.0 


1199.3 


2.108 


.4744 


218 


220 


389.9 


363.1 


836.4 


1199.5 


2.090 


.4787 


220 


222 


390.7 


363.9 


835.7 


1199.6 


2.072 


.4829 


222 


224 


391.5 


364.7 


835.0 


1199.7 


2.054 


.4870 


224 


226 


392.2 


365.5 


834.3 


1199.8 


2.037 


.4910 


226 


228 


393.0 


366.3 


833.7 


1200.0 


2.020 


.4950 


228 


230 


393.8 


367.1 


833.0 


1200.1 


2.003 


.4992 


230 


232 


394.5 


367.9 


832.3 


1200.2 


1.987 


.503 


232 


234 


395.2 


368.6 


831.7 


1200.3 


1.970 


.507 


234 


236 


396.0 


369.4 


831.0 


1200.4 


1.954 


.511 


236 


238 


396.7 


370.2 


830.4 


1200.6 


1.938 


.516 


238 


240 


397.4 


371.0 


829.8 


1200.8 


1.923 


.520 


240 


242 


398.2 


371.7 


829.2 


1200.9 


1.907 


.524 


242 


244 


398.9 


372.5 


828.5 


1201.0 


1.892 


.528 


244 


246 


399.6 


373.3 


827.8 


1201.1 


1.877 


.532 


246 


248 


400.3 


374.0 


827.2 


1201.2 


1.862 


.537 


248 


250 


401.1 


374.7 


" 826.6 


1201.3 


1.848 


.541 


250 


275 


409.6 


383.7 


819.0 


1202.7 


1.684 


.594 


275 


300 


417.5 


392.0 


811.8 


1203.8 


1.547 


.647 


300 


350 


431.9 


407.4 


798.5 


1205.9 


1.330 


.750 


350 



APPENDIX 



409 



TABLE II 

Properties of Common Substances 



Specific 

Gravity. 



Weight 
per 
Cubic 
Foot, 
Lbs. 



Weight 
of One 
Cubic 
Inch, 
Lb. 



Specific 
Heat. 



Coefficient of Expan- 
sion per Deg. F. 



Volu- 
metric. 



Aluminum 

Bismuth 

Brass 

Copper 

Coal (anthracite) . . 

Coke 

Gasoline 

Glass 

Gold 

Ice (at. 32° F.) . . . . 

Iron (cast) 

Iron (wrought) . . . 

Lead 

Limestone 

Mercury (at 32° F.) 

Cement 

Nickel 

Platinum 

Pine (white) 

Silver 

Steel 

Tin 

Zinc 



2.60 

9.82 
8.10 
8.79 
1.43 
1.00 
.68 
2.89 

19.26 
.92 
7.5 
7.74 

11.35 
3.16 

13.60 
2.24 
8.90 

21.5 
.55 

10.47 
7.83 
7.29 
7.19 



161. 

613. 

503. 

545. 
88.7 
62.4 
42.4 

180.7 
1200. 
57.5 

465. 

582. 

708. 

197. 

849. 

140. 

547. 

1342. 

34. 

653. 

486. 

452. 

445. 



.095 
.353 
.293 
.318 
.058 
.037 

.105 
.697 
.033 
.271 
.280 
.411 
.114 
.492 
.083 
.321 
.779 
.020 
.379 
.292 
.264 
.260 



.212 
.031 
.094 
.092 
.241 
.203 

.198 

.032 

.504 

.130 

.114 

.031 

.217 

.033 

.20 

.109 

.032 

.65 

.056 

.116 

.056 

.095 



.000011 
.000008 
.00001 
.000009 



.000005 
.000008 

.000006 
.000007 
.000016 

.000033 

.000008 

.000007 

.000005 

.0000025 

.000011 

.000007 

.000012 

.000016 



.000033 
.000024 
.00003 
.000028 



.000014 
.000024 

.000018 
.000021 
.000048 

.000100 
.000024 
.000020 
.000015 
.000008 
.000033 
.000020 
.000035 
.000048 



INDEX 



PAGE 

Absorption Refrigerating Machines 345 

Air Compressors, Testing of 334 _ 336 

Air Engines 350 

Air, Flow of 142 



Air " Horse Power. 



33o 



Air, Velocity and Volume of 143, 330 

Air Supplied to Furnace, Determination of, from Flue Gases 194 

Alden Brake Dynamometer I2 8 

Allen-Moyer Gas Apparatus i 9I 

Alternating Current, Measurement of 282, 294 

Ammonia, Leakage of 342 

Ammonia, Properties of, Tables 341-342 

Ammonia Refrigerating Plants 339 

Amsler Planimeter 66 

Analysis of Coal, Proximate 1 78, 2 1 1 

Analysis of Flue Gases 181, 212 

Analysis of Flue Gases, Typical Examples of 187 

Anemometers !47 

Areas, Measurement of 66, 120 

Ash in Fuel, Determination of ! 80 

Aspirator ! 83 

Atwater's Fuel Calorimeter ^7 

Available Energy 266 

Averager (Planimeter) , Amsler 66 

Averager (Planimeter), Coffin ^5 

Bachelder Indicator n c 

Back-firing Indicator Diagrams ^7 

Balance-sheet of Gas Engine -, I . 

Balance-sheet of Boiler 214, 223 

Balance-sheet of Steam Engine 257 

Barraclough & Mark's Engine Tests 274 

Belts, Testing Tension in ■, r . 

Bending (Transverse) Tests 300 

Blowers, Testing of , 2 s 

Boiler Balance-sheet 214, 223 

411 



412 INDEX 

PAGE 

Boiler Efficiency ' 213, 221 

Boiler Feed-pumps, Testing of 356, 358 

Boiler Feed- water, Measurement of, in Tests 205 

Boiler Heat Balance 214, 223 

Boiler Horse Power 201 

Boiler Summary Sheets 215 

Boiler Test Log Sheet ." 202 

Boiler Testing : Datum Lines of Water and Fire in Tests 207 

Boiler Testing, Principal Objects of 200 

Boiler Testing, Rules for (A. S. M. E.) 202 

Bourdon Pressure Gage, Theory of 5,6 

Bourdon Pressure Gage with Steel Tube 7 

Brake Dynamometers 122-129 

Brake Horse Power 126, 306 

Brake Pulley, Design for 127 

Briquettes of Neat Cement and Mortar for Testing 399-401 

Bristol-Durand Integrator for Circular Diagrams 11, 80 

Brumbo's Pulley 115 

Burning Point of Oils, How Tested 311 

Calibration of Pressure Gages 12 

" Vacuum " 21 

" Indicator Springs 104 

Thermo-Electric Thermometers and Pyrometers 38 

" Mercury Thermometers 26 

Calorific Value of Fuel, Determination of 162, 177 

Calorific Value of Gas . 1 74 

Calorimeter, Barrel (for Steam) 62 

' ' , Bomb (for Fuels) ,. 163 

' ' , Combined Separating and Throttling 57~6o 

' ' , Condensing (Steam) 46, 62 

' ' , Calibration of *. 65 

' ' , Electric 61 

' ' , Fuel 162 

' ' , Junkers 1 74 

' ' , Separating (Steam) 56 

Throttling 46 

' ' , Wire-drawing (or Throttling) 46 

' ' Charts for Determining Moisture in Steam 50, 54 

Nipples 48 

Capillary Corrections for Mercury 4 

Carbonic Acid (C0 2 ) Apparatus for Determining 188, 191, 196 

Carbonic Acid Refrigerating Machine 340- 

Cement Tests 395 

Centrifugal Fans, Testing of 325 

' ' Pumps, Testing of 362 

Chemical Analysis of Fuels to Determine Calorific Value 177; 



INDEX 413 

PAGE 

Chimney Gases, Weight of, Calculated from Analysis 225 

Clearance of an Engine Cylinder, Determination of 240 

Coal Analysis 178 

Coal, Calorific Value of, from Analysis 177 

Coals Recommended for Standard Boiler Trials (A. S. M. E.) 204 

Coal Testing: Proximate Analysis 178 

Coal Calorimeters 162 

Coefficient of Dilution 192 

Discharge for Orifices 158 

Weirs 161 

Expansion of Mercury 19 

Coefficients of Expansion of Various Substances Appendix 

" of Friction of Friction Wheels 355 

Coffin Planimeter 75 

Columns, Testing of 389 

Combined Separating and Throttling Calorimeters 57 

Commercial Steam Engine Testing 244 

' ' Turbine Testing 281 

Compression Tests of Materials 387 

Compressors, Air, Testing of 334 

' ' , Ammonia, Testing of 346 

Condensers, Testing of 243 

Continuous Indicator 99 

Conversion of Pressures 3 

' ' Temperatures and Heat Units 26 

Cooley-Hill Continuous Indicator 99 

Cooley Indicator Spring Tester 105 

Cooley Stroke Measuring Counter 361 

Corliss Engine Diagrams, Normal and Abnormal 235, 251 

Corliss Engine Valve-setting 234 

Correcting Steam Engine and Steam Turbine Tests to Standard Con- 
ditions 296 

Correction Curves for a Steam Turbine 297 

Correction for Stem Exposure of Mercury Thermometers 31 

Crosby Indicator 88 

Curve, Hyperbolic as Applied to Indicator Diagram 250 

' ' , Typical ' ' Error " 21 

Curves for Determinations of Moisture in Steam 50, 54 

Cut-off, How Determined 250 

Dead-center to Set Engine On 231 

Dead-weight Gage Testers 13 

Deflectometers 380 

Density of Water at Different Temperatures 4 

' ' Ammonia (Liquid) 34 1 

' ' Substances, Table of Appendix 

Diagram Factor of Engines : 252 



414 INDEX 

PAGE 

Differential Dynamometer, Calibration of 137 

Direct Current, Measurement of 293 

Draft Gages 23 

Ducts, Loss of Velocity in 333 

" , Measuring Velocity of Air in 143, 330 

Durand-Bristol Integrator 1 1 , 80 

Duty of a Steam Pump 357 

Dynamometer, Alden 128 

, Differential 134 

, Dynamo 131 

, Emerson "Scales" 133 

, Flather 140 

, Hints on Management 124-125 

, Rope and Strap 126 

, Water Brake : 128 

, Webber Transmission 136 

Eccentric, Setting of, Effect on Indicator Diagram 235 

Econometer 198 

Economy of Steam Engine Compared with Ideal 253 

Efficiency of Steam Boiler 213, 221 

' ' Fans or Blowers 330 

Gas Engine 310, 314 

' ' Gas Producer 324 

Refrigerating Machines 343 

Steam Engines 259 

" " Turbines 286 

' ' Compared with Rankine Cycle 287 

Ejector for Flue Gases 183 

Elastic Limit Defined 380 

Electric Dynamometers 131 

Electrical Measurement of Power 293 

' ' Instruments, Precautions to be Observed 294 

' ' Pyrometers 36 

Emerson Fuel Calorimeter 168 

' ' Power Scales 138 

Engine and Boiler Tests 245 

Engine Lubricators 276 

Engine Test, Balance-sheet 259 

Entropy Defined 262 

Entropy Diagram of Rankine Cycle 267 

Entropy-temperature Diagrams 262-268 

Extensometer 379 

Fans, Ventilating 325 

Feed- water, Measurement of 242, 246 

' ' , Thermometer and Gage 44 



INDEX 415 

PAGE 

Feed Pumps, Testing of 356, 358 

Flashing Point of Oil, How Determined : 311 

Flather's Dynamometer 140 

Fliegner's Formula 334 

Flow of Air 143-148, 334 

' ' Steam 148 

" Water 150 

Flue Gas Analysis 181 

Flue Gas, Determination of Air Supply from . 194 

Flue Gases, Loss of Heat in 214, 225 

' ' , Weight of 225 

Form for Report of Boiler Test 215 

Gas Engine Test 311 

Steam Engine Test 254 

" Pump Test 360 

Francis Formula for Weirs 160 

Friction Brakes and Dynamometers 122 

' ' Horse Power , 229 

' ' Wheels, Tests of 355 

Fuel: Calculation of Heating Value 166, 177 

Fuel Calorimeters 163 

Fuel for Gas and Oil Engines, Measurement of 308, 310 

Fuels, Calorific Value of t 162 

Fuel Testing 162, 178 



Gages, Bourdon 6 

, Calibration of 12 

, Diaphragm , 8 

, Pressure 6 

, Recording 10 

, Vacuum 2,9 

Gage Notch 1 59 

Gage Testers 13 

Gas, Calorific Value of 1 74 

' ' , Measurement of 142, 308 

Gas Engine Balance Sheet 314, 324 

" , Efficiency of 310, 314 

' ' Fuel, Measurement 310, 312 

" Indicator Diagrams: Normal, "Suction," etc. 316 

showing "Timing" of Ignition 318 

Gas Fuels 318 

' ' Meters 142 

' ' Producers 310 

Gasoline, Measurement of 308, 310 

Goss Dynamometer 133 

" Guarantee " Tests 286 



416 



INDEX 



Head at a Pump (Suction, Discharge, Total), Denned 357 

Heat Balance of Boiler 214, 223 

Gas Engine 314 

Steam Engine 257 

Refrigerating Plant 347 

Heat Units, Conversion of 26 

Heating Value of Fuels Calculated from Analysis 177 

by Experiment 162 

Heat Unit Basis of Engine Testing 246, 260 

Hoists, Efficiency of 353 

Hook Gage , 1 59 

Horse Power, Boiler 201 

, Brake 126 

, Indicated 118, 247, 306 

Hot-air Engine, Testing of . : 351 

Humidity of Air 331 

Hydraulic Machinery, Testing of 356 

Hydraulic Motors, Testing of 363 

' ' Rams, Testing of 367 

Hyperbolic Curve Applied to Engine Indicator Diagrams 250 



Impellers of Fans 327 

Impulse Water Wheels .• 363 

Indicated Horse Power, Calculation of 118, 247, 306 

Engine Constant 121 

Indicator, Bachelder 95 

Care of 97 

Continuous 99 

Crosby 88 

Crosby Gas Engine 308 

High-pressure (Ordnance) , 335 

Optical 101 

" Star Brass " 93 

Tabor 93 

Thompson 85 

Watt 85 

Indicator Diagrams, Analysis of 249 

, Calculation of Steam Consumption from 272 

from Flather's Dynanometer 141 

of Gas and Oil Engines 315 

showing Back Firing 317 

of Suction Stroke 316 

Taken with Light Spring Attachment 316 

Indicator Testing Apparatus 112 

Spring Testing 105 

' ' , Calibration of 104 

Injector, Method of Operating • 373 



INDEX 417 

TAGE 

Injector, Testing 372 

Test, Form for Report on 374 

" Used in Boiler Testing, Correction Applied to Feed-water 205 

Integating Instruments, Durand-Bristol 80 

, Planimeters . .' 66-78 

"Internal" Horse Power 286 

Junkers Gas Calorimeter 1 74 

Latent Heat of Ammonia 342 

Steam, Table of Appendix 

Leakage Test of a Boiler 242 

' ' of Steam in Tests 241 

Light Spring Indicator Diagrams of Suction Stroke of Gas Engine 316 

Log Form for Indicator Spring Test 1 1 1 

' ' for Mechanical Efficiency Test of Engine 230 

' ' for Pressure Gage Test 20 

' ' for Thermometer Calibration 28, 31 

Losses of Head in Ducts 333 

Low Heat Value of Gas 176 

Lubricators, Engine 276 

Mahler Bomb Calorimeter 164 

Machines for Testing Strength of Materials 376-398 

Manometers 1-4 

Mean Ordinate, Determination of 78, 120 

' ' Effective Pressure by Coffin Planimeter 78 

Mechanical Pyrometer 38 

Efficiency '. 229, 307, 330, 335 

Mercury Columns, Cleaning of 4 

' ' , Corrections for 4 

' ' and Equivalent Pressure per Unit Area 3 

' ' Column for Calibrating Gages 18, 22 

' ' , Expansion of 19 and Appendix 

Meter, Gas 143 

' ' , Venturi 155 

Modulus of Elasticity 381 

Moisture in Coal 178 

Steam (by Charts) 50, 54 

' ' , Determination of 46 

Mortar, Testing of . 400 

Moulds for Cement Briquettes 396 

Napier's Formula ; . 148 

Oil Engines, Measurement of Fuel for 308 

"Orsat" Apparatus 188 



418 INDEX 

PACE 

Optical Pyrometers 39 

Pantograph Reducing Motion for Indicators _ 115 

Parallel Rule for Dividing Diagrams 120 

Parr Calorimeters 169 

Pendulum Reducing Motions 113 

Permanent "Set" Denned 380 

Perry Optical Indicator 102 

Pitot Tubes 143, 330 

Planimeter, Amsler 66 

Calibration of 79 

' ' , Coffin 75 

' ' , Polar, Theory of 67 

, Roller 78 

Positive Pressure Blowers 328 

Power, Measurement of 122 

Power Scales, Emerson 138 

Pressure (lbs. per square inch) and Equivalent Head of Water or of Air . 3 

Pressure and Temperature of Steam, Table of Append'x 

Pressure Type of Gas Producer 319 

Pressure Gages > 5 

j> " . , for Measuring Draft 23 

" , Calibration of . . . 12, 18 

' , Recording 10 

Pressure Gage Tester, Dead-weight 13 

Pressure Scales, Crosby 17 

Prony Brake ...... • - 122 

Proximate Analysis of Coal !.............. 1 78 

Pulsometer, Testing of 370 

Pump, Centrifugal, Testing of 359 

Pumping Engine Trials 357, 360 

Pumps, Effective Head at 357 

' ' , Testing of Feed 356, 358 

Pyrometer, Calibration of 38 

' ' , Calorimetric 41 

Cones 43 

' ' , Electric Resistance 37 

' ' , Mechanical 38 

' ' , Mercury 38 

' ' , Optical . . . ! 39 

5 ' , Radiation 40 

" , Recording 38 

' ' , Thermo-electric 36 



Quality of Steam, How Calculated 49 

' ' Determined from Charts 50, 54 



INDEX 419 

PAGE 

Radiation Loss in Calorimeters 55, 162, 166, 173 

Rankine Cycle Steam Engines and Turbines 253, 261, 287 

Ratio of Expansion 252 

Reaction Water Turbines 366 

Recording CO2 Apparatus. 196 

' ' Gages 10 

' ' Thermometers 34 

' ' Pyrometers 38 

Reducing Motions for Indicators 1 13-1 18 

Refrigerating Plants 337 

Capacity 344 

Report of Boiler Test, Forms for 215 

' ' Gas Engine Test, Forms for 311 

' ' Steam Engine Test, Forms for 254 

Resilience 381 

Rider Hot Air Engine 350 

Rope Brake 126 

' ' , Hints on Management of (footnote) 125 

Rope Drives, Tension in 354 

Rotation Losses in Turbines 289 

Rules for Boiler Testing (A. S. M. E.) 202 

Gas Engine Testing (A. S. M. E.) 310 

' ' Steam Engine Testing (A. S. M. E.) 241 

Sampling Bottle for Flue Gases 182 

Sampling Coal . ., 210 

Tubes for Flue Gas (A. S. M. E.) 184 

Scales for Weighing Fuel . 206, 309 

Seger Pyrometer Cones 43 

Separating Calorimeter 56 

" Set " (Permanent) Defined 380 

Siphons for Steam Gages 7 

Sirocco Fans 326 

Slip in Pumps 357 

Smoke Observations 212 

Specific Gravities of Various Substances, Table of Appendix 

Specific Heat of Ammonia 342 

" Various Substances, Table of Appendix 

" Superheated Steam 270 

' ' Volume of Steam Appendix 

Speed-output Curves 281, 288 

Spring Tester, Indicator 104 

Standard Conditions for Ventilating Fans (U. S. Navy) 333 

Engine and Turbine Tests 296 

' ' Gases 176, 324 

Steam,. Flow of 148 

Steam Calorimeters 4 6_6 5 



420 INDEX 

PAGE 

Steam Consumption Calculated from Indicator Diagram 272 

Determined from Feed- water 242 

when Using Surface Condenser 24^ 

Calculated from Heat Balance 285 

Steam Engine Balance-sheet 257 

Lubricators 276 

Testing, Rules for 241 

Thermal Efficiency of 259 

Steam Measurement 242 

" Tables of Properties of 29, Appendix 

Stem Exposure of -Thermometers, Correction for 31 

Stroke-measuring Counter 361 

Suction Gas Producer, Testing of 319 

" Stroke Diagrams of a Gas Engine 316 

" Head of Pump, Measurement of with Gage (footnote) 360 

Superheated Ammonia 341 

Steam, Flow of 149 

" Specific Heat of 270 

Tabor Indicator , 93 

Temperature-entropy Diagrams 253 

Temperature, Measurement of 25 

Scales, Conversion of 26 

Tension Tests of Materials 379, 382 

Testing Boilers 200 

" Gas Engines 306 

" Hydraulic Motors 356 

" Impulse Water Wheels _ 363 

" Refrigerating Machines 337, 341 

" Steam Engines 229 

" " Pumps 360 

" " Turbines 279 

" Strength of Materials 376 

" Ventilating Fans and Blowers ^. . . . 328 

" Water Turbines 366 

Test-pieces, Standard Shapes and Sizes for 382, 396 

Thermal Efficiency of a Boiler 221 

" Gas Engine , 310, 314 

" " Steam Engine 259 

" " " Turbine 286 

Thermo-electric Pyrometers and Thermometers 36 

Thermometer, Alcohol 26 

" and Pressure Gage Combined , 44 

" Calibration of 26, 51 

" Correction for Stem Exposure 31 

" for Flue Gases 36 

" High Temperatures (footnote), ... 29, 38 






INDEX 421 

PAGE 

Thermometer, Mercury 25 

' ' , Recording 34 

with Mercury Well for Steam Pipes 44 

" , Regraduating of (footnote) 25 

" , Standard 26 

" , Thermo-electric 36 

, Wet and Dry Bulb 331 

Thompson Indicator 85 

Throttling Calorimeters 46 

Timing of Ignition 318 

Torque (footnote) 122 

" of Steam Turbine 289 

Total Heat of Saturated Steam, Table of Appendix 

" " Superheated Steam 270 

Trammels, Method of, for Setting Engine on Dead Center 231 

Transmission Dynamometers 135-140 

Transverse Bending Tests 390 

Turbine Dynamometer, Westinghouse 130 

Ultimate Strength Defined 381 

Vacuum Gages 2-3, 9 

on Suction Pipes of Pumps (footnote) 360 

Valve Setting, D-slide and Piston Types . 230 

, Corliss Type 234 

Velocity of Air 143, 330 

Ventilating Fans 325 

' ' Systems, Testing of 332 

Venturi Water Meter . . . . _ 155 

Volatile Matter in Coal 179 

Volume of Air Discharged by a Blower 330 

" of a Pound of Steam, Table of Appendix 

Volumetric Efficiency of Refrigerating Machine 343 

Water Brake 128 

' ' Cooled Brake Pulley 127 

' ' Equivalent of Calorimeters 64, 162 

' ' Flow through Circular Orifice or Nozzle 156 

' ' Friction Dynamometer, Westinghouse 130 

' ' Measurement of by Weir 159 

' ' Measuring Tank, Continuous 152 

' ' Meters 150 

' ' Meter, Venturi 155 

* ' Rate Curve 281 

* ' Turbines 366 

" ' , Weight of at Different Temperatures 4 

' ' Wheels, Testing of . . 363 



422 INDEX 



PAGE 

Watt's Indicator. 85 

Weak Spring Indicator Diagrams 316 

Webber's Transmission Dynamometer 136 

Weighing Machine, for Water 152. 

Weight of Air Required to Burn a Pound of Fuel 194, 225, 228 

Weight of Air, Table of 145 

' ' Chimney Gases 225 

' ' Flue Gases 225 

' ' a Cubic Foot of Steam, Table of Appendix 

' ' Various Substances, Table of Appendix 

Water at Different Temperatures 4 

Westinghouse Water Brake 130 

Wet and Dry Bulb Thermometer for Humidity 331 

Willan's Law 274 

Lines 274, 276, 283, 309 

Wire-drawing Calorimeters 46 



SEP 14 1911 



